Liquid crystal medium and liquid crystal display

ABSTRACT

The instant invention relates to mesogenic media exhibiting a blue phase, comprising one, two or more compounds of formula I-A 
                         
wherein the parameters are as specified in the text, preferably stabilised by a polymer, and their use in electro-optical light modulation elements and their respective use in displays, as well as to such displays.

FIELD OF THE INVENTION

The present invention relates to compounds, media comprising thesecompounds and to electro-optical displays comprising these media aslight modulation media. Preferably the compounds of the presentinvention are mesogenic compounds and they are preferably used in liquidcrystalline media. In particular the electro-optical displays accordingto the present invention are displays, which are operated at atemperature, at which the mesogenic modulation media are in an opticallyisotropic phase, preferably in a blue phase.

Problem to be Solved and State of the Art

Electro-optical displays and mesogenic light modulation media, which arein the isotropic phase when being operated in the display are describedin DE 102 17 273 A. Electro-optical displays, and mesogenic lightmodulation media, which are in the optically isotropic blue phase, whenbeing operated in the display are described in WO 2004/046 805.

is e.g. mentioned in EP 1 006 109 A1.

Compounds of the formulae

are e.g. proposed for liquid crystalline media for IPS displays in WO2008/128623 A1.

EP 2 302 015 A1 shows the use of

as well as of

in a simple nematic host mixture and the use of

in a dielectrically positive liquid crystal mixture, comprising thechiral compound

which exhibits a blue phase and is stabilized by photo-polymerization ofa reactive mesogen of the formula

WO 2010/058681 A1 mentions, amongst other compounds,

which exhibit a nematic phase, and also optically isotropic liquidcrystalline media comprising these compounds besides other compoundssuch as e.g.

U.S. Pat. No. 7,070,838 describes polymerisable compounds containing a2-di- or trifluoromethyl-1,4-phenyl ring, and the use thereof inpolymerisable mixtures, LC polymers and LC displays having a cholestericphase and in optical films. Specific compounds of a formula 1a-2-19having the following structure are also disclosed therein

However, no properties of this compound on use in an LC display aredisclosed. In addition, the use of such compounds for the stabilisationof blue phases or in PSA displays is neither described in nor is obviousfrom U.S. Pat. No. 7,070,838.

JP 2005-015473 A discloses polymerisable compounds containingunsaturated spacer groups (alkynylene or alkenylene). Specific compoundsof the formulae 1-13-77 to 1-13-84, 1-13-134, 1-13-135, 1-56-9, 1-56-10,1-56-23, 1-56-24 which contain phenyl rings linked via CF₂O bridges arealso disclosed therein, as is the use thereof for the production ofoptically anisotropic films and in ferroelectric LC media. Specificcompounds, for example having the following structures, are alsodisclosed therein.

However, the use of such compounds for the stabilisation of blue phasesor in PSA displays is neither described in nor is obvious from JP2005-015473 A.

The specifications US 2009/0268143 and US 2010/0078593 claimdifluorooxymethylene-bridged polymerisable compounds containing a ringsystem having negative dielectric anisotropy as a component inliquid-crystal mixtures for anisotropic films.

However, no properties of these compounds on use in an LC display aredisclosed. In addition, the use of such compounds for the stabilisationof blue phases or in PSA displays is neither described in nor is obviousfrom these specifications.

The mesogenic media and displays described in these references provideseveral significant advantages compared to well-known and widely useddisplays using liquid crystals in the nematic phase, like for exampleliquid crystal displays (LCDs) operating in the twisted nematic (TN)-,the super twisted nematic (STN)-, the electrically controlledbirefringence (ECB)-mode with its various modifications and the in-planeswitching (IPS)-mode.

Amongst these advantages are most pronounced their much faster switchingtimes, and significantly wider optical viewing angle.

Whereas, compared to displays using mesogenic media in another liquidcrystalline phase, as e.g. in the smectic phase in surface stabilizedferroelectric liquid crystal displays (SSF LCDs), the displays of DE 10217 273.0 and WO 2004/046 805 are much easier to manufacture. Forexample, they do not require a very thin cell gap and in addition theelectro-optical effect is not very sensitive to small variations of thecell gap.

However, the liquid crystal media described in these patent applicationsmentioned still require operating voltages, which are not low enough forsome applications. Further the operating voltages of these media varywith temperature, and it is generally observed, that at a certaintemperature the voltage dramatically increases with increasingtemperature. This limits the applicability of liquid crystal media inthe blue phase for display applications. A further disadvantage of theliquid crystal media described in these patent applications is theirmoderate reliability which is insufficient for very demandingapplications. This moderate reliability may be for example expressed interms of the voltage holding ratio (VHR) parameter, which in liquidcrystal media as described above may be below 90%.

Some compounds and compositions have been reported which possess a bluephase between the cholesteric phase and the isotropic phase that canusually be observed by optical microscopy. These compounds orcompositions for which the blue phases are observed are typically singlemesogenic compounds or mixtures showing a high chirality. However,generally the blue phases observed only extend over a very smalltemperature range, which is typically less than 1 degree centigradewide, and/or the blue phase is located at rather inconvenienttemperatures.

In order to operate the novel fast switching display mode of WO 2004/046805 the light modulation medium to be used has to be in the blue phaseover a broad range of temperatures encompassing ambient temperature,however. Thus, a light modulation medium possessing a blue phase, whichis as wide as possible and conveniently located is required.

Therefore there is a strong need for a modulation medium with a bluephase with a wide phase range, which may be achieved either by anappropriate mixture of mesogenic compounds themselves or, preferably bymixing a host mixture with appropriate mesogenic properties with asingle dopant or a mixture of dopants that stabilises the blue phaseover a wide temperature range.

Summarizing, there is a need for liquid crystal media, which can beoperated in liquid crystal displays, which are operated at temperatureswhere the media is in the blue phase, which provide the followingtechnical improvements:

-   -   a reduced operating voltage,    -   a reduced temperature dependency of the operating voltage and    -   an improved reliability, e.g. VHR.        Present Invention

Surprisingly, it now has been found that mesogenic media exhibiting ablue phase and comprising one, two or more compounds of formula I-A,preferably in a total concentration of 1% or more to 30% or less,preferably to 25% or less,

wherein

-   R¹ is alkyl, which is straight chain or branched, preferably has 1    to 20 C-atoms, is unsubstituted, mono- or poly-substituted by F, Cl    or CN, preferably by F, and in which one or more CH₂ groups are    optionally replaced, in each case independently from one another, by    —O—, —S—, —NR⁰¹—, —SiR⁰¹R⁰²—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—,    —CO—S—, —CY⁰¹═CY⁰²— or —C≡C— in such a manner that O and/or S atoms    are not linked directly to one another, preferably n-alkyl or    n-alkoxy with 1 to 9 C-atoms, preferably with 2 to 5 C-atoms,    alkenyl, alkenyloxy or alkoxyalkyl with 2 to 9 C-atoms, preferably    with 2 to 5 C-atoms or halogenated alkyl, halogenated alkenyl or    halogenated alkoxy with preferably up to 9 C-atoms, preferably mono    fluorinated, di-fluorinated or oligofluorinated alkyl, alkenyl or    alkoxy with preferably up to 9 C-atoms, most preferably n-alkyl,    n-alkoxy, alkenyl, alkenyloxy or alkoxyalkyl with preferably up to 9    C-atoms,-   L¹¹ and L¹² are, independently of each other, H or F, preferably one    is F and the other H or F and most preferably both are F,-   Y⁰¹ and Y⁰² are, independently of each other, F, Cl or CN, and    alternatively one of them may be H, and

R⁰¹ and R⁰² are, independently of each other, H or alkyl with 1 to 12C-atoms,

amongst which chiral compounds are encompassed, too, allow to realizemedia with an acceptably high clearing point and/or a rather highstability of the voltage holding ratio against temperature and/orUV-load and in particular against the latter.

At the same time the resultant media are characterized by an extremelyhigh value of Δ∈, a very high value of product (Δ∈·Δn) and also by afavourably low viscosity and a good stability at deep temperatures.

In a preferred embodiment of the present invention the mesogenic mediacomprise compounds of formula I-A in a concentration from 2% or more,preferably from 3% or more and most preferably from 5% or more to 20% orless, preferably to 16% or less and most preferably to 14% or less.

In this embodiment the mesogenic media comprise component A preferablyin a total concentration from 5% or more, preferably from 7% or more to20% or less, preferably to 15% or less.

Preferably the compounds of formula I-A are selected from the compoundsof formula I-A-1 and I-A-2, preferably from formula I-A-2

wherein R¹ has the meaning given under formula I-A above.

In a further preferred embodiment of the present invention the mesogenicmedia comprise one more compounds of formula I-E

-   L⁰¹ to L⁰³ are independently of one another H or F, preferably L⁰¹    is F and/or L⁰² is F,-   R⁰ is alkyl, which is straight chain or branched, is unsubstituted,    mono- or poly-substituted by F, Cl or CN, preferably by F, and in    which one or more CH₂ groups are optionally replaced, in each case    independently from one another, by —O—, —S—, —NR⁰¹—, —SiR⁰¹R⁰²—,    —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CY⁰¹═CY⁰²— or —C≡C— in    such a manner that O and/or S atoms are not linked directly to one    another,-   Y⁰¹ and Y⁰² are, independently of each other, F, Cl or CN, and    alternatively one of them may be H,-   R⁰¹ and R⁰² are, independently of each other, H or alkyl with 1 to    12 C-atoms, and-   n is 0 or 1.

In this preferred embodiment of the present invention the mesogenicmedia preferably comprise one more compounds of formula I-E-1,preferably in a concentration of 2% to 15%,

and/or one more compounds of formula I-E-2, preferably in aconcentration of 4% to 20%,

wherein R⁰ has the meaning given under formula I-E above and preferablyis n-alkyl, most preferably ethyl, n-propyl, n-butyl, n-pentyl, orn-hexyl or n-heptyl, most preferably ethyl or n-propyl.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula I-T

wherein

-   R¹ has the meaning given under formula I-A above and-   L¹ is H or F, preferably F.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula I-T selected from the group ofcompounds of formulae I-T-1 and I-T-2

wherein

-   R¹ has the meanings given under formula I-T above and preferably is    n-alkyl, most preferably ethyl, n-propyl, n-butyl, n-pentyl or    n-hexyl.

In a further preferred embodiment of the present invention the mesogenicmedia comprise one more compounds of formula I-N

wherein

-   R¹, L¹ and n have the meanings given under formulae I-A, I-E, and    I-T, respectively, above.

In a further preferred embodiment of the present invention the mesogenicmedia comprise one more compounds of formula I-N selected from the groupof compounds of formulae I-N-1 and I-N-2

wherein

-   R¹ has the meanings given under formula I-N above and preferably is    n-alkyl, most preferably ethyl, n-propyl, n-butyl, n-pentyl or    n-hexyl.

It has been further been found that mesogenic media, which arecomprising, additionally to the compound or the compounds of formula I-Aand optionally I-T, I-N and/or I-E, or of their respective preferredsub-formulae, one or more compounds of formula II

wherein

-   m is 0 or 1,-   L²¹ to L²³ are, independently of each other, H or F, preferably L²¹    and L²² are both F and/or L²³ is F,-   R² is alkyl, which is straight chain or branched, preferably has 1    to 20 C-atoms, is unsubstituted, mono- or poly-substituted by F, Cl    or CN, preferably by F, and in which one or more CH₂ groups are    optionally replaced, in each case independently from one another, by    —O—, —S—, —NR⁰¹—, —SiR⁰¹R⁰²—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—,    —CO—S—, —CY⁰¹═CY⁰²— or —C≡C— in such a manner that O and/or S atoms    are not linked directly to one another, preferably n-alkyl or    n-alkoxy with 1 to 9 C-atoms, preferably with 2 to 5 C-atoms,    alkenyl, alkenyloxy or alkoxyalkyl with 2 to 9 C-atoms, preferably    with 2 to 5 C-atoms or halogenated alkyl, halogenated alkenyl or    halogenated alkoxy with preferably up to 9 C-atoms, preferably mono    fluorinated, di-fluorinated or oligofluorinated alkyl, alkenyl or    alkoxy with preferably up to 9 C-atoms, most preferably n-alkyl,    n-alkoxy, alkenyl, alkenyloxy or alkoxyalkyl with preferably up to 9    C-atoms,-   Y⁰¹ and Y⁰² are, independently of each other, F, Cl or CN, and    alternatively one of them may be H,-   R⁰¹ and R⁰² are, independently of each other, H or alkyl with 1 to    12 C-atoms,    amongst which chiral compounds are encompassed, too, allow to    realize media with an acceptably high clearing point and/or a rather    high stability of the voltage holding ratio against temperature    and/or UV-load and in particular against the latter.

In a preferred embodiment of the present invention the media accordingto the present invention additionally comprise one more compounds offormula III

wherein

-   R³ has the meaning given for R¹ under formula I-A above.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula III, preferably one or morecompounds wherein R³ has the meaning given under formula III above andmore preferably is n-alkyl, more preferably ethyl, n-propyl, n-butyl,n-pentyl or n-hexyl and, most preferably n-butyl.

Preferably the media according to the present invention additionallycomprise one more compounds selected from the group of compounds offormulae IV and V

wherein

-   R⁴ and R⁵ are, independently of each other, alkyl, which is straight    chain or branched, preferably has 1 to 20 C-atoms, is unsubstituted,    mono- or poly-substituted by F, Cl or CN, preferably by F, and in    which one or more CH₂ groups are optionally replaced, in each case    independently from one another, by —O—, —S—, —CO—, —COO—, —OCO—,    —OCO—O—, —S—CO—, —CO—S— or —C≡C— in such a manner that O and/or S    atoms are not linked directly to one another, preferably n-alkyl or    n-alkoxy with 1 to 9 C-atoms, preferably 2 to 5 C-atoms, alkenyl,    alkenyloxy or alkoxyalkyl with 2 to 9 C-atoms, preferably with 2 to    5 C-atoms, most preferably n-alkyl, n-alkoxy, alkenyl, alkenyloxy or    alkoxyalkyl with preferably up to 9 C-atoms,-   L⁵ is H or F, preferably F,

is

preferably

and

-   n and m are, independently of one another, 0 or 1, preferably m is    1.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula II, preferably selected from thegroup of compounds of its sub-formulae II-1 to II-8, preferably offormula II-1 to II-4, most preferably of formula II-3,

wherein R² has the meaning given under formula II above and preferablyis n-butyl or n-pentyl.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula IV, preferably selected from thegroup of compounds of its sub-formulae IV-1 to IV-3, preferably offormula IV-3,

wherein R⁴ has the meaning given under formula IV above.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula V, preferably selected from thegroup of compounds of its sub-formulae V-1 and V-2, preferably one ormore compounds of formula V-1 and one or more compounds of formula V-2,

wherein R⁵ and L⁵ have the meanings given under formula V above.

An alkyl or an alkoxy radical, i.e. an alkyl where the terminal CH₂group is replaced by —O—, in this application may be straight-chain orbranched. It is preferably straight-chain, has 1, 2, 3, 4, 5, 6, 7 or 8carbon atoms and accordingly is preferably methyl, ethyl, propyl, butyl,pentyl, hexyl, heptyl, octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy,heptoxy, or octoxy, furthermore nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, nonoxy, decoxy, undecoxy, dodecoxy,tridecoxy or tetradecoxy, for example.

Oxaalkyl, i.e. an alkyl group in which one non-terminal CH₂ group isreplaced by —O—, is preferably straight-chain 2-oxapropyl(=methoxy-methyl), 2- (=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl),2-, 3-, or 4-oxapentyl, 2-, 3-, 4-, or 5-oxahexyl, 2-, 3-, 4-, 5-, or6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or8-oxanonyl or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl, for example.

An alkenyl group, i.e. an alkyl group wherein one or more CH₂ groups arereplaced by —CH═CH—, may be straight-chain or branched. It is preferablystraight-chain, has 2 to 10 C atoms and accordingly is preferably vinyl,prop-1-, or prop-2-enyl, but-1-, 2- or but-3-enyl, pent-1-, 2-, 3- orpent-4-enyl, hex-1-, 2-, 3-, 4- or hex-5-enyl, hept-1-, 2-, 3-, 4-, 5-or hept-6-enyl, oct-1-, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, non-1-, 2-,3-, 4-, 5-, 6-, 7- or non-8-enyl, dec-1-, 2-, 3-, 4-, 5-, 6-, 7-, 8- ordec-9-enyl.

Especially preferred alkenyl groups are C₂-C₇-1E-alkenyl,C₄-C₇-3E-alkenyl, C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, inparticular C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl.Examples for particularly preferred alkenyl groups are vinyl,1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl,3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl,4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groupshaving up to 5 C-atoms are generally preferred.

In an alkyl group, wherein one CH₂ group is replaced by —O— and one by—CO—, these radicals are preferably neighboured. Accordingly theseradicals together form a carbonyloxy group —CO—O— or an oxycarbonylgroup —O—CO—. Preferably such an alkyl group is straight-chain and has 2to 6 C atoms.

It is accordingly preferably acetyloxy, propionyloxy, butyryloxy,pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl,butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl,2-propionyloxy-ethyl, 2-butyryloxyethyl, 3-acetyloxypropyl,3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl,ethoxy-carbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl,2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl,3-(ethoxycarbonyl)propyl, 4-(methoxycarbonyl)-butyl.

An alkyl group wherein two or more CH₂ groups are replaced by —O— and/or—COO—, it can be straight-chain or branched. It is preferablystraight-chain and has 3 to 12 C atoms. Accordingly it is preferablybis-carboxy-methyl, 2,2-bis-carboxy-ethyl, 3,3-bis-carboxy-propyl,4,4-bis-carboxy-butyl, 5,5-bis-carboxy-pentyl, 6,6-bis-carboxy-hexyl,7,7-bis-carboxy-heptyl, 8,8-bis-carboxy-octyl, 9,9-bis-carboxy-nonyl,10,10-bis-carboxy-decyl, bis-(methoxycarbonyl)-methyl,2,2-bis-(methoxycarbonyl)-ethyl, 3,3-bis-(methoxycarbonyl)-propyl,4,4-bis-(methoxycarbonyl)-butyl, 5,5-bis-(methoxycarbonyl)-pentyl,6,6-bis-(methoxycarbonyl)-hexyl, 7,7-bis-(methoxycarbonyl)-heptyl,8,8-bis-(methoxycarbonyl)-octyl, bis-(ethoxycarbonyl)-methyl,2,2-bis-(ethoxycarbonyl)-ethyl, 3,3-bis-(ethoxycarbonyl)-propyl,4,4-bis-(ethoxycarbonyl)-butyl, 5,5-bis-(ethoxycarbonyl)-hexyl.

A alkyl or alkenyl group that is monosubstituted by CN or CF₃ ispreferably straight-chain. The substitution by CN or CF₃ can be in anydesired position.

An alkyl or alkenyl group that is at least monosubstituted by halogen,it is preferably straight-chain. Halogen is preferably F or Cl, in caseof multiple substitution preferably F. The resulting groups include alsoperfluorinated groups. In case of monosubstitution the F or Clsubstituent can be in any desired position, but is preferably inω-position. Examples for especially preferred straight-chain groups witha terminal F substituent are fluoromethyl, 2-fluoroethyl,3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and7-fluoroheptyl. Other positions of F are, however, not excluded.

Halogen means F, Cl, Br and I and is preferably F or Cl, most preferablyF. Each of R¹ to R⁵ and R⁰ may be a polar or a non-polar group. In caseof a polar group, it is preferably selected from CN, SF₅, halogen, OCH₃,SCN, COR⁵, COOR⁵ or a mono- oligo- or polyfluorinated alkyl or alkoxygroup with 1 to 4 C atoms. R⁵ is optionally fluorinated alkyl with 1 to4, preferably 1 to 3 C atoms. Especially preferred polar groups areselected of F, Cl, CN, OCH₃, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, CHF₂,CH₂F, OCF₃, OCHF₂, OCH₂F, C₂F₅ and OC₂F₅, in particular F, Cl, CN, CF₃,OCHF₂ and OCF₃. In case of a non-polar group, it is preferably alkylwith up to 15 C atoms or alkoxy with 2 to 15 C atoms.

Each of R¹ to R⁵ and R⁰ may be an achiral or a chiral group. In case ofa chiral group it is preferably of formula I*:

wherein

-   Q¹ is an alkylene or alkylene-oxy group with 1 to 9 C atoms or a    single bond,-   Q² is an alkyl or alkoxy group with 1 to 10 C atoms which may be    unsubstituted, mono- or polysubstituted by F, Cl, Br or CN, it being    also possible for one or more non-adjacent CH₂ groups to be    replaced, in each case independently from one another, by —C≡C—,    —O—, —S—, —NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO— or    —CO—S— in such a manner that oxygen atoms are not linked directly to    one another,-   Q³ is F, Cl, Br, CN or an alkyl or alkoxy group as defined for Q²    but being different from Q².

In case Q¹ in formula I* is an alkylene-oxy group, the O atom ispreferably adjacent to the chiral C atom.

Preferred chiral groups of formula I* are 2-alkyl, 2-alkoxy,2-methylalkyl, 2-methylalkoxy, 2-fluoroalkyl, 2-fluoroalkoxy,2-(2-ethin)-alkyl, 2-(2-ethin)-alkoxy, 1,1,1-trifluoro-2-alkyl and1,1,1-trifluoro-2-alkoxy.

Particularly preferred chiral groups I* are 2-butyl (=1-methylpropyl),2-methylbutyl, 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl,2-propylpentyl, in particular 2-methylbutyl, 2-methylbutoxy,2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy,2-octyloxy, 2-oxa-3-methylbutyl, 3-oxa-4-methylpentyl, 4-methylhexyl,2-hexyl, 2-octyl, 2-nonyl, 2-decyl, 2-dodecyl, 6-methoxyoctoxy,6-methyloctoxy, 6-methyloctanoyloxy, 5-methylheptyloxycarbonyl,2-methylbutyryloxy, 3-methylvaleroyloxy, 4-methylhexanoyloxy,2-chlorpropionyloxy, 2-chloro-3-methylbutyryloxy,2-chloro-4-methylvaleryloxy, 2-chloro-3-methylvaleryloxy,2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl, 1-methoxypropyl-2-oxy,1-ethoxypropyl-2-oxy, 1-propoxypropyl-2-oxy, 1-butoxypropyl-2-oxy,2-fluorooctyloxy, 2-fluorodecyloxy, 1,1,1-trifluoro-2-octyloxy,1,1,1-trifluoro-2-octyl, 2-fluoromethyloctyloxy for example. Verypreferred are 2-hexyl, 2-octyl, 2-octyloxy, 1,1,1-trifluoro-2-hexyl,1,1,1-trifluoro-2-octyl and 1,1,1-trifluoro-2-octyloxy.

In addition, compounds containing an achiral branched alkyl group mayoccasionally be of importance, for example, due to a reduction in thetendency towards crystallization. Branched groups of this type generallydo not contain more than one chain branch. Preferred achiral branchedgroups are isopropyl, isobutyl (=methylpropyl), isopentyl(=3-methylbutyl), isopropoxy, 2-methyl-propoxy and 3-methylbutoxy.

Preferably the liquid crystalline media according to the presentinvention comprise one or more reactive compounds, respectivelypolymerisable compounds, each comprising one, two or more reactivegroups, respectively polymerizable groups. The mesogenic materialpreferably is stabilized in the blue phase by the formation of apolymer, which may have the form of a matrix or of a network.

For use in a display application, the temperature range of typicalmaterials, which are exhibiting a pure blue phase (BP) on their own,generally is not wide enough. Such materially typically have a bluephase, which extends over a small temperature range of only somedegrees, e.g. about 3 to 4°. Thus, an additional stabilisation,extending the temperature range of the blue phase, is needed in order tomake such material suitable for practical applications such as indisplays.

In order to stabilise the blue phase by the formation of a polymer, theformulated blue phase host mixture is conveniently combined with anappropriate chiral dopant (one or more suitable chiral compounds) andwith one or more reactive compounds, preferably reactive mesogeniccompounds (RMs). The resultant mixture is filled into the LC cellrespectively display panel. The LC cell/panel is then held at a certaintemperature at which the mixture is in the blue phase, e.g. it is heatedor cooled until blue phase can be observed at a certain temperature.This temperature is maintained during the whole polymerisation process.The polymerisation process is typically controlled by UV irradiation ofa typical medium-pressure mercury-vapour lamp. A standard condition ise.g. use of 3 mW/cm² for 180 sec. at a wavelength of 380 nm. To avoiddamage to the LC material appropriate optical filters can be usedadditionally.

In the following the criteria for stability of the obtained polymerstabilised blue phase (BP) are briefly be explained.

Ensuring an excellent quality of the polymer stabilisation is criticalfor use of PS-BP in a display application. The quality of polymerstabilization is the judged by several criteria. Optical inspectionensures a good polymerisation. Any defect and/or haziness observed inthe test cell/panel is an indication of an suboptimal polymerstabilisation. Electro-optical inspection under various load/stressconditions ensures long-time stability of the PS-BP. A typical displayparameter is the so-called memory effect (ME). The memory effect isdefined as the ratio of the contrast ratio for switching on and of thecontrast ratio for switching off as a normalized measure of the residualtransmission after one or more switching cycles have been executed. Avalue for this memory effect of 1.0 is an indicator of an excellentpolymer stabilisation. A value for this memory effect of more than 1.1indicates insufficient stabilisation of the blue phase.

The present invention further relates to an LC medium comprising one ormore compounds selected from the group of the compounds of formula I-Aand optionally of the formulae I-E, I-T, I-N, II III, IV, V, one or morechiral dopants and one or more compounds of the formula PP^(a)-(Sp^(a))_(s1)-(A¹-Z¹)_(n1)-A²-Q-A³-(Z⁴-A⁴)_(n2)-(Sp^(b))_(s2)-P^(b)  Pwherein the individual radicals have the following meanings:

-   P^(a), P^(b) each, independently of one another, are a polymerisable    group,-   Sp^(a), Sp^(b) each, independently of one another, denote a spacer    group,-   s1, s2 each, independently of one another, denote 0 or 1,-   n1, n2 each, independently of one another, denote 0 or 1, preferably    0,-   Q denotes —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —(CO)O—, —O(CO)—,    —(CH₂)₄—, —CH₂CH₂—, —CF₂—CF₂—, —CF₂—CH₂—, —CH₂—CF₂—, —CH═CH—,    —CF═CF—, —CF═CH—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CF—, —C≡C—, —O—, —CH₂—,    —(CH₂)₃—, —CF₂—, preferably —CF₂O—,-   Z¹, Z⁴ denote a single bond, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—,    —(CO)O—, —O(CO)—, —(CH₂)₄—, —CH₂CH₂—, —CF₂—CF₂—, —CF₂—CH₂—,    —CH₂—CF₂—, —CH═CH—, —CF═CF—, —CF═CH—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CF—,    —C≡C—, —O—, —CH₂—, —(CH₂)₃—, —CF₂—, where Z¹ and Q or Z⁴ and Q do    not simultaneously denote a group selected from —CF₂O— and —OCF₂—,-   A¹, A², A³, A⁴ each, independently of one another, denote a    diradical group selected from the following groups:    -   a) the group consisting of trans-1,4-cyclohexylene,        1,4-cyclohexenylene and 1,4′-bicyclohexylene, in which, in        addition, one or more non-adjacent CH₂ groups may be replaced by        —O— and/or —S— and in which, in addition, one or more H atoms        may be replaced by F,    -   b) the group consisting of 1,4-phenylene and 1,3-phenylene, in        which, in addition, one or two CH groups may be replaced by N        and in which, in addition, one or more H atoms may be replaced        by L,    -   c) the group consisting of tetrahydropyran-2,5-diyl,        1,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl,        cyclobutane-1,3-diyl, piperidine-1,4-diyl, thiophene-2,5-diyl        and selenophene-2,5-diyl, each of which may also be mono- or        polysubstituted by L,    -   d) the group consisting of saturated, partially unsaturated or        fully unsaturated, and optionally substituted, polycyclic        radicals having 5 to 20 cyclic C atoms, one or more of which        may, in addition, be replaced by heteroatoms, preferably        selected from the group consisting of        bicyclo[1.1.1]pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl,        spiro[3.3]heptane-2,6-diyl,

-   -    where, in addition, one or more H atoms in these radicals may        be replaced by L, and/or one or more double bonds may be        replaced by single bonds, and/or one or more CH groups may be        replaced by N,

-   L on each occurrence, identically or differently, denotes F, Cl, CN,    SCN, SF₅ or straight-chain or branched, in each case optionally    fluorinated, alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl,    alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms,

-   R⁰³, R⁰⁴ each, independently of one another, denote H, F or    straight-chain or branched alkyl having 1 to 12 C atoms, in which,    in addition, one or more H atoms may be replaced by F,

-   M denotes —O—, —S—, —CH₂—, —CHY¹— or —CY¹Y²—, and

-   Y¹ and Y² each, independently of one another, have one of the    meanings indicated above for R⁰, or denote Cl or CN, and one of the    groups Y¹ and Y² alternatively denotes —OCF₃, preferably H, F, Cl,    CN or CF₃,    as well as to a polymer stabilized system obtainable by    polymerisation of one or more compounds of the formula P alone or in    combination with on or more further polymerisable compounds from a    respective mixture, and to the use of such a stabilized system in    electro-optical displays having a blue phase.

Compounds of the formula P used preferably according to the presentinvention are selected from the group consisting of the followingformulae:

in which L in each occurrence, identically or differently, has one ofthe meanings indicated above and below, r denotes 0, 1, 2, 3 or 4, sdenotes 0, 1, 2 or 3, and n denotes an integer between 1 and 24,preferably between 1 and 12, very particularly preferably between 2 and8, and in which, if a radical is not indicated at the end of a single ordouble bond, it is a terminal CH₃ or CH₂ group.

In the formulae P1 to P24,

preferably denotes a group selected from the group consisting of thefollowing formulae:

particularly preferably

The group A²-Q-A³ preferably denotes a group of the formula

in which at least one of the rings is substituted by at least one groupL=F. r here is in each case, independently, preferably 0, 1 or 2.

P^(a) and P^(b) in the compounds of the formula P and the sub-formulaethereof preferably denote acrylate or methacrylate, furthermorefluoroacrylate. Sp^(a) and Sp^(b) in the compounds of the formula I andthe sub-formulae thereof preferably denote a radical selected from thegroup consisting of —(CH₂)_(p1)—, —(CH₂)_(p1)—O—, —(CH₂)_(p1)—O—CO— and—(CH₂)_(p1)—O—CO—O— and mirror images thereof, in which p1 denotes aninteger from 1 to 12, preferably from 1 to 6, particularly preferably 1,2 or 3, where these groups are linked to P^(a) or P^(b) in such a waythat O atoms are not directly adjacent.

Of the compounds of the formula P, particular preference is given tothose in which

-   -   the radicals P^(a) and P^(b) are selected from the group        consisting of vinyloxy, acrylate, methacrylate, fluoroacrylate,        chloroacrylate, oxetane and epoxide groups, particularly        preferably acrylate or methacrylate groups,    -   the radicals Sp^(a) and Sp^(b) are selected from the group        consisting of —(CH₂)_(p1)—, —(CH₂)_(p1)—O—, —(CH₂)_(p1)—O—CO—        and —(CH₂)_(p1)—O—CO—O— and mirror images thereof, in which p1        denotes an integer from 1 to 12, preferably from 1 to 6,        particularly preferably 1, 2 or 3, and where these radicals are        linked to P^(a) or P^(b) in such a way that O atoms are not        directly adjacent, Compounds of formula P preferably used        according to a preferred embodiment of the instant invention are        those comprising exactly two rings (n1=n2=0), which are        preferably 6-membered rings. Especially preferred are compounds        selected from the group of compounds of the following formulae:

wherein P^(a), P^(b), Sp^(a), Sp^(b), s1 and s2 are as defined underformula P above, and preferably Sp^(a/b) is alkylene —(CH₂)_(n)— whereinn preferably is 3, 4, 5, 6 or 7 and P^(a/b) preferably a methacrylat- oracrylate moiety. Especially preferred is the use of compounds selectedfrom the group of formulae Pa, Pb, Pc, Pd, Pe, Pf, Pg, Ph and Pi and, inparticular the compounds of formula Pa.

In formula P the moiety “A²-Q-A³” preferably is a moiety of formula

wherein preferably at least one of the two phenylene rings issubstituted by at least one L, which is different from H, wherein r isindependently for each ring, and preferably it is for each ring 0, 1 or2.

For the compounds of formula P, as well as for its respectivesub-formulae, preferably

-   P^(a) and P^(b) are, independently from each other, acrylate or    methacrylate, but also fluoroacrylate,-   Sp^(a) and Sp^(b) are, independently from each other, —(CH₂)_(p1)—,    —(CH₂)_(p1)—O—, —O—(CH₂)_(p1)—, —(CH₂)_(p1)—O—CO—,    —CO—O—(CH₂)_(p1)—, —(CH₂)_(p1)—O—CO—O— or —(CH₂)_(p1)—O—CO—O—,    wherein p1 is an integer from 1 to 12, preferably from 1 to 6,    particularly preferred 1, 2 or 3, and wherein these moieties are    linked with P^(a) or P^(b) in such a way that no O-atoms are linked    directly to one another.

Especially preferred is the use of compounds of formula P, wherein

-   -   P^(a) and P^(b) are vinyleoxy-, acrylate-, methacrylata-,        fluoroacrylate-, chloroacrylate-, oxetane- or an epoxygroup,        particularly preferred acrylate- or methacrylate,    -   Sp^(a) and Sp^(b) are —(CH₂)_(p1)—, —(CH₂)_(p1)—O—,        —O—(CH₂)_(p1)—, —(CH₂)_(p1)—O—CO—, —CO—O—(CH₂)_(p1)—,        —(CH₂)_(p1)—O—CO—O— or —(CH₂)_(p1)—O—CO—O—, wherein p1 is an        integer from 1 to 12, preferably from 1 to 6, particularly        preferred 1, 2 or 3, and wherein these moieties are linked with        P^(a) or P^(b) in such a way that no O-atoms are linked directly        to one another.

For the production of polymer stabilised displays according to thepresent invention, the polymerisable compounds are polymerised orcrosslinked, in case one compound contains or more compounds contain twoor more polymerisable groups, by in-situ polymerisation in the LC mediumbetween the substrates of the LC display with application of a voltage.The polymerisation can be carried out in one step. It is preferable tocarry out the polymerisation at a temperature at which the material,i.e. the mesogenic mixture comprising the chiral compounds and thepolymer precursor are in the blue phase.

Suitable and preferred polymerisation methods are, for example, thermalor photopolymerisation, preferably photopolymerisation, in particular UVphotopolymerisation. One or more initiators can optionally also be addedhere. Suitable conditions for the polymerisation and suitable types andamounts of initiators are known to the person skilled in the art and aredescribed in the literature. Suitable for free-radical polymerisationare, for example, the commercially available photoinitiatorsIrgacure651®, Irgacure184®, Irgacure907®, Irgacure369® or Darocure1173®(Ciba AG). If an initiator is employed, its proportion is preferably0.001 to 5% by weight, particularly preferably 0.001 to 1% by weight.

The polymerisable compounds according to the invention are also suitablefor polymerisation without an initiator, which is accompanied byconsiderable advantages, such as, for example, lower material costs andin particular less contamination of the LC medium by possible residualamounts of the initiator or degradation products thereof. Thepolymerisation can thus also be carried out without the addition of aninitiator. In a preferred embodiment, the LC medium thus comprises nopolymerisation initiator.

The polymerisable component or the LC medium may also comprise one ormore stabilisers in order to prevent undesired spontaneouspolymerisation of the RMs, for example during storage or transport.Suitable types and amounts of stabilisers are known to the personskilled in the art and are described in the literature. Particularlysuitable are, for example, the commercially available stabilisers fromthe Irganox® series (Ciba AG), such as, for example, Irganox® 1076. Ifstabilisers are employed, their proportion, based on the total amount ofRMs or the polymerisable component, is preferably in the range from 10to 10,000 ppm, particularly preferably in the range from 50 to 2,000ppm, most preferably 0.2% or about 0.2%.

The polymerisable compounds of formula P used preferably according tothe present invention can be polymerised individually, but it is alsopossible to polymerise mixtures which comprise two or more polymerisablecompounds according to the invention, or mixtures comprising one or morepolymerisable compounds according to the invention and one or morefurther polymerisable compounds (comonomers), which are preferablymesogenic or liquid-crystalline. In the case of polymerisation of suchmixtures, copolymers form. A mixture of two or more compounds accordingto the invention or a mixture comprising one or more compounds accordingto the invention with one or more further polymerisable compounds ispreferably used. The invention furthermore relates to the polymerisablemixtures mentioned above and below. The polymerisable compounds andcomonomers are mesogenic or non-mesogenic, preferably mesogenic orliquid-crystalline.

Suitable and preferred co-monomers for use in polymer precursors forpolymer stabilised displays according to the invention are selected, forexample, from the following formulae:

wherein the parameters have the following meanings:

-   P¹ and P² each, independently of one another, a polymerisable group,    preferably having one of the meanings given above or below for    P^(a), particularly preferred an acrylate, methacrylate,    fluoroacrylate, oxetane, vinyloxy- or epoxy group,-   Sp¹ and Sp² each, independently of one another, a single bond or a    spacer group, preferably having one of the meanings given above or    below for Sp^(a), particularly preferred an —(CH₂)_(p1)—,    —(CH₂)_(p1)—O—, —(CH₂)_(p1)—CO—O— or —(CH₂)_(p1)—O—CO—O—, wherein p1    is an integer from 1 to 12, and wherein the groups mentioned last    are linked to the adjacent ring via the O-atom,    and, wherein alternatively also one or more of P¹-Sp¹- and P²-Sp²-    may be R^(aa), provided that at least one of P¹-Sp¹- and P²-Sp²-    present in the compound is not R^(aa),-   R^(aa) H, F, Cl, CN or linear or branched alkyl having 1 to 25    C-atoms, wherein one or more non-adjacent —CH₂— groups,    independently of each another, may be replaced by —C(R⁰)═C(R⁰⁰)—,    —C≡C—, —N(R⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O— in such a    way that neither O- nor S-atoms are directly linked to one another,    and wherein also one or more H-atoms may be replaced by F, Cl, CN or    P¹-Sp¹-, particularly preferred linear or branched, optionally    single- or polyfluorinated, alkyl, alkoxy, alkenyl, alkinyl,    alkylcarbonyl, alkoxycarbonyl, or alkylcarbonyloxy having 1 to 12    C-atoms, wherein the alkenyl- and alkinyl groups have at least two    and the branched groups have at least three C-atoms,-   R⁰, R⁰⁰ each, at each occurrence independently of one another, H or    alkyl having 1 to 12 C-atoms,-   R^(y) and R^(z) each, independently of one another, H, F, CH₃ or    CF₃,-   Z¹ —O—, —CO—, —C(R^(y)R^(z))—, or —CF₂CF₂—,-   Z² and Z³ each, independently of one another, —CO—O—, —O—CO—,    —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—, or —(CH₂)_(n)—, wherein n is 2, 3 or    4,-   L at each occurrence independently of one another, F, Cl, CN, SCN,    SF₅ or linear or branched, optionally mono- or polyfluorinated,    alkyl, alkoxy, alkenyl, alkinyl, alkylcarbonyl, alkoxycarbonyl,    alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C-atoms,    preferably F,-   L′ and L″ each, independently of one another, H, F or Cl,-   r 0, 1, 2, 3 or 4,-   s 0, 1, 2 or 3,-   t 0, 1 or 2, and-   x 0 or 1.

Suitable and preferred co-monomers for use in displays according to thepresent application operable and/or operating at a temperature where themesogenic medium is in the blue are for example selected from the groupof mono-reactive compounds, which are present in the precursor of thepolymer stabilised systems in a concentration in the range from 1 to 9wt.-%, particularly preferred from 4 to 7 wt.-%. Preferred mono-reactivecompounds are the compounds of formulae M1 to M29, wherein one or moreof P¹-Sp¹- and P²-Sp²- are Rest R^(aa), such that the compounds have asingle reactive group only.

Particularly preferred mono-reactive compounds are the compounds of thefollowing formulae

wherein P¹, Sp¹ and R^(aa) have the respective meanings given above.

Amongst these the compounds of the formula

wherein

-   n is an integer, preferably an even integer, in the range from 1 to    16, preferably from 2 to 8,-   m is an integer in the range from 1 to 15, preferably from 2 to 7,    are especially preferred.

Particular preference is given to an LC medium, an LC display, a processor the use as described above and below in which the LC medium or thepolymerisable or polymerised component present therein comprises one ormore compounds of the following formula:

in which P^(a), P^(b), Sp^(a), Sp^(b), s1, s2 and L have the meaningsindicated above and below, r denotes 0, 1, 2, 3 or 4, and Z² and Z³each, independently of one another, denote —CF₂—O— or —O—CF₂—,preferably Z² is —CF₂—O— and Z³ is —O—CF₂— or vice versa, and, mostpreferably, Z² is —CF₂—O— and Z³ is —O—CF₂—.

The compounds of formula I are accessible by the usual methods known tothe expert. Starting materials may be, e.g., compounds of the followingtypes, which are either commercially available or accessible bypublished methods.

Preferably the liquid crystalline media according to the instantinvention contain a component A comprising, preferably predominantlyconsisting of and most preferably entirely consisting of compounds offormulae I-A, I-E, I-T and I-N.

Comprising in this application means in the context of compositions thatthe entity referred to, e.g. the medium or the component, contains thecompound or compounds in question, preferably in a total concentrationof 10% or more and most preferably of 20% or more.

Predominantly consisting, in this context, means that the entityreferred to contains 80% or more, preferably 90% or more and mostpreferably 95% or more of the compound or compounds in question.

Entirely consisting, in this context, means that the entity referred tocontains 98% or more, preferably 99% or more and most preferably 100.0%of the compound or compounds in question.

The concentration of the compounds according to the present applicationcontained in the media according to the present application preferablyis in the range from 0.5% or more to 70% or less, more preferably in therange from 1% or more to 60% or less and most preferably in the rangefrom 5% or more to 50% or less.

In a preferred embodiment the mesogenic modulation media according tothe instant invention comprise

-   -   one compound or more compounds of formula I-A, preferably in a        total concentration of 1% to 30% by weight, more preferably in a        concentration of 2% to 25% by weight, and/or    -   one compound or more compounds of formula I-T, preferably in a        total concentration of 50% to 70% by weight, more preferably in        a concentration of 55% to 65% by weight, and        -   preferably in a concentration of each single compound from            3% to 17%, more preferably from 5% to 15% by weight for each            single compound present, and/or    -   one compound or more compounds of formula I-N, preferably in a        total concentration of 10% to 45% by weight, more preferably in        a concentration of 15% to 40% by weight, and        -   preferably in a concentration of each single compound from            1% to 17%, more preferably from 3% to 15% by weight for each            single compound present, and/or    -   one compound or more compounds of formula I-E, preferably in a        total concentration of 3% to 30% by weight, more preferably in a        concentration of 5% to 25% by weight, and most preferably        -   in a concentration of case of 1% to 15%, more preferably            from 3% to 11% by weight for each single compound present,            and/or    -   optionally, preferably obligatorily, one or more compounds        selected from the group of compounds of formulae IV and V, if        present, preferably in a concentration of 1% to 15% by weight,        and/or    -   of one or more chiral compounds with a HTP of ≧20 νm⁻¹,        preferably in a concentration of 1% to 20% by weight, and/or    -   optionally, preferably obligatorily, a polymer precursor,        comprising reactive compounds, preferably comprising reactive        mesogens, which, upon polymerisation, are able to, and        preferably do stabilize the phase range of the blue phase and/or        decrease the temperature dependence of the electro-optical        effect, preferably in a concentration in the range from 5% or        more to 15% or less, preferably from 7% or more to 12% or less        and most preferably from 8% or more to 11% or less.

In this application, unless explicitly stated otherwise

-   -   the concentrations of the constituents of the host mixtures are        given with respect to the total host mixture, i.e. excluding the        chiral dopant(s) and the polymer precursor,    -   the concentrations of the chiral dopant(s) are given with        respect to the total host including mixture the chiral dopant(s)        but excluding the polymer precursor,    -   the concentrations of polymer precursor and its constituents are        given with respect to the total mixture total, i.e. the mixture        consisting of the host mixture, the chiral dopant(s) and the        polymer precursor,

The inventive mixtures preferably comprise one or more compounds offormula I-A in a total concentration in the range from 2% or more to 30%or less, preferably from 3% or more to 20% or less and most preferablyfrom 5% or more to 14% or less.

The inventive mixtures preferably comprise one or more compoundsselected from the group of compounds of formulae I-T and I-N andoptionally I-E, preferably in a total concentration in the range from10% or more to 80% or less, preferably from 20% or more to 70% or lessand most preferably from 35% or more to 55% or less.

In particular, the inventive mixtures preferably comprise one or morecompounds of formula I-T in a total concentration in the range from 10%or more to 70% or less, preferably from 30% or more to 60% or less andmost preferably from 35% or more to 55% or less.

In particular, the inventive mixtures preferably comprise one or morecompounds of formula I-N in a total concentration in the range from 3%or more to 30% or less, preferably from 5% or more to 25% or less andmost preferably from 5% or more to 20% or less.

In case the inventive mixtures comprise one or more compounds formulaI-E-1, the total concentration of these compounds preferably is in therange from 1% or more to 35% or less, preferably from 3% or more to 30%or less and most preferably from 4% or more to 25% or less.

In case the inventive mixtures comprise one or more compounds formulaI-E-2, the total concentration of these compounds preferably is in therange from 1% or more to 35% or less, preferably from 3% or more to 30%or less and most preferably from 4% or more to 25% or less.

In case the inventive mixtures comprise one or more compounds formula Vthe total concentration of these compounds preferably is in the rangefrom 1% or more to 15% or less, preferably from 2% or more to 10% orless and most preferably from 5% or more to 8% or less.

Suitable chiral compounds are those, which have an absolute value of thehelical twisting power of 20 μm⁻¹ or more, preferably of 40 μm⁻¹ or moreand most preferably of 60 μm⁻¹ or more. The HTP is measured in theliquid crystalline medium MLC-6260 at a temperature of 20° C.

The mesogenic media according to the present invention comprisepreferably one or more chiral compounds which have a mesogenic structureand exhibit preferably one or more meso-phases themselves, particularlyat least one cholesteric phase. Preferred chiral compounds beingcomprised in the mesogenic media are, amongst others, well known chiraldopants like cholesteryl-nonanoate (CN), R/S-811, R/S-1011, R/S-2011,R/S-3011, R/S-4011, R/S-5011, CB-15 (Merck KGaA, Darmstadt, Germany).Preferred are chiral dopants having one or more chiral moieties and oneor more mesogenic groups or having one or more aromatic or alicyclicmoieties forming, together with the chiral moiety, a mesogenic group.More preferred are chiral moieties and mesogenic chiral compoundsdisclosed in DE 34 25 503, DE 35 34 777, DE 35 34 778, DE 35 34 779, DE35 34 780, DE 43 42 280, EP 01 038 941 and DE 195 41 820 that disclosureis incorporated within this application by way of reference. Particularpreference is given to chiral binaphthyl derivatives as disclosed in EP01 111 954.2, chiral binaphthol derivatives as disclosed in WO 02/34739,chiral TADDOL derivatives as disclosed in WO 02/06265 as well as chiraldopants having at least one fluorinated linker and one end chiral moietyor one central chiral moiety as disclosed in WO 02/06196 and WO02/06195.

The mesogenic medium of the present invention has a characteristictemperature, preferably a clearing point, in the range from about +30°C. to about 90° C., especially up to about 70° C. or even 80° C.

The inventive mixtures preferably contain one or more (two, three, fouror more) chiral compounds in the range of 1-25 wt. %, preferably 2-20wt. %, each. Especially preferred are mixtures containing 3-15 wt.-%total of one or more chiral compounds.

Preferred embodiments are indicated below:

-   -   the medium comprises one, two, three, four or more compounds of        formula I-T, preferably of formula I-T-1 and/or 1-T-2, and/or    -   the medium comprises one, two, three, four or more compounds of        formula I-N, preferably of formula I-N-1 and/or 1-N-2, and/or    -   the medium comprises one, two, three, four or more compounds of        formula I-E, preferably of formula I-E-1, and/or    -   the medium comprises one, two or more compounds of formula II,        preferably of formula II-3, and/or    -   the medium comprises one or more compounds of formula III and/or    -   the medium comprises one, two or more compounds of formula IV,        preferably of formula IV-2, and/or    -   the medium comprises one, two, three or more compounds of        formula V, and/or    -   the medium comprises one, two, three or more chiral compounds,        preferably having a helical twisting power of 20 μm⁻¹ or more,        and/or    -   the medium comprises one, two or more reactive compounds,        preferably one two or more reactive mesogenic compounds,        preferably of formulae P, preferably of one or more of its        sub-formulae, and/or one or more reactive mesogenic compounds        selected from the group of formulae M1 to M29, preferably of        formulae M16-A and/or M17-A, more preferably of formula M17-A′.

It has been found that even a relatively small proportion of compoundsof the formula I-A mixed with conventional liquid-crystal materials, butin particular with one or more compounds of the formulae II and III,leads to a lower operating voltage and a broader operating temperaturerange. Preference is given, in particular, to mixtures which, besidesone or more compounds of the formula I-A, comprise one or more compoundsof the formula III, in particular compounds of the formula III in whichR³ is n-butyl.

The compounds of the formulae I-A, I-T, I-N, I-E and II to V arecolourless, stable and readily miscible with one another and with otherliquid-crystalline materials.

The optimum mixing ratio of the compounds of the formulae I-A, I-T, I-N,I-E and II to V depends substantially on the desired properties, on thechoice of the components of the formulae I-A, I-T, I-N and/or I-E, andII to V, and on the choice of any other components that may be present.Suitable mixing ratios within the range given above can easily bedetermined from case to case.

The total amount of compounds of the respective individual formulae I-A,I-T, I-N, I-E and II to V in the mixtures according to the invention isin many cases not crucial, as long as the total amount of compounds is85% or more.

The mixtures can therefore comprise one or more further components forthe purposes of optimisation of various properties. However, theobserved effect on the operating voltage and the operating temperaturerange is generally greater, the higher the total concentration ofcompounds of the formulae I-A and optionally I-T and/or I-N and/oroptionally I-E.

The individual compounds of the formulae I-A, I-T, I-N, I-E and II to V,which can be preferably used in the media according to the invention,are either known or can be prepared analogously to the known compounds.

The construction of the MLC display according to the invention frompolarisers, electrode base plates and surface-treated electrodescorresponds to the conventional construction for displays of this type.The term conventional construction is broadly drawn here and also coversall derivatives and modifications of the MLC display, in particularincluding matrix display elements based on poly-Si TFT or MIM, however,particularly preferred are displays, which have electrodes on just oneof the substrates, i.e. so called inter-digital electrodes, as thoseused in IPS displays, preferably in one of the established structures.

A significant difference between the displays according to the inventionand the conventional displays based on the twisted nematic cellconsists, however, in the choice of the liquid-crystal parameters of theliquid-crystal layer.

The media according to the invention are prepared in a mannerconventional per se. In general, the components are dissolved in oneanother, advantageously at elevated temperature. By means of suitableadditives, the liquid-crystalline phases in accordance with theinvention can be modified in such a way that they can be used in alltypes of liquid crystal display elements that have been disclosedhitherto. Additives of this type are known to the person skilled in theart and are described in detail in the literature (H. Kelker and R.Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). Forexample, pleochroic dyes can be added for the preparation of colouredguest-host systems or substances can be added in order to modify thedielectric anisotropy, the viscosity and/or the alignment of the nematicphases. Furthermore, stabilisers and antioxidants can be added.

The mixtures according to the invention are suitable for TN, STN, ECBand IPS applications and isotropic switching mode (ISM) applications.Hence, there use in an electro-optical device and an electro-opticaldevice containing liquid crystal media comprising at least one compoundaccording to the invention are subject matters of the present invention.

The inventive mixtures are highly suitable for devices, which operate inan optically isotropic state. The mixtures of the invention aresurprisingly found to be highly suitable for the respective use.

Electro-optical devices that are operated or operable in an opticallyisotropic state recently have become of interest with respect to video,TV, and multi-media applications. This is, because conventional liquidcrystal displays utilizing electro-optical effects based on the physicalproperties of liquid crystals exhibit a rather high switching time,which is undesired for said applications. Furthermore most of theconventional displays show a significant viewing angle dependence ofcontrast that in turn makes necessary measures to compensate thisundesired property.

With regard to devices utilizing electro-optical effects in an isotropicstate the German Patent Application DE 102 17 273 A1 for examplediscloses light-controlling (light modulation) elements in which themesogenic controlling medium for modulation is in the isotropic phase atthe operating temperature. These light controlling elements have a veryshort switching time and a good viewing angle dependence of contrast.However, the driving or operating voltages of said elements are veryoften unsuitably high for some applications.

German Patent Application DE 102 41 301 A1 describes specific structuresof electrodes allowing a significant reduction of the driving voltages.However, these electrodes make the process of manufacturing the lightcontrolling elements more complicated.

Furthermore, the light controlling elements, for example, disclosed inboth DE 102 17 273 A1 and DE 102 41 301 show significant temperaturedependence. The electro-optical effect that can be induced by theelectrical field in the controlling medium being in an optical isotropicstate is most pronounced at temperatures close to the clearing point ofthe controlling medium. In this range the light controlling elementshave the lowest values of their characteristic voltages and, thus,require the lowest operating voltages. As temperature increases, thecharacteristic voltages and hence the operating voltages increaseremarkably. Typical values of the temperature dependence are in therange from about a few volts per centigrade up to about ten or morevolts per centigrade. While DE 102 41 301 describes various structuresof electrodes for devices operable or operated in the isotropic state,DE 102 17 273 A1 discloses isotropic media of varying composition thatare useful in light controlling elements operable or operated in theisotropic state. The relative temperature dependence of the thresholdvoltage in these light controlling elements is at a temperature of 1centigrade above the clearing point in the range of about50%/centigrade. That temperature dependence decreases with increasingtemperature so that it is at a temperature of 5 centigrade above theclearing point of about 10%/centigrade. However, for many practicalapplications of displays utilizing said light controlling elements thetemperature dependence of the electro-optical effect is too high. To thecontrary, for practical uses it is desired that the operating voltagesare independent from the operating temperature over a temperature rangeof at least some centi-grades, preferably of about 5 centi-grades ormore, even more preferably of about 10 centi-grades or more andespecially of about 20 centi-grades or more.

Now it has been found that the use of the inventive mixtures are highlysuitable as controlling media in the light controlling elements asdescribed above and in DE 102 17 273 A1, DE 102 41 301 A1 and DE 102 53606 A1 and broaden the temperature range in which the operating voltagesof said electro-optical operates. In this case the optical isotropicstate or the blue phase is almost completely or completely independentfrom the operating temperature.

This effect is even more distinct if the mesogenic controlling mediaexhibit at least one so-called “blue phase” as described in WO 2004/046805 A1.

Liquid crystals having an extremely high chiral twist may have one ormore optically isotropic phases. If they have a respective cholestericpitch, these phases might appear bluish in a cell having a sufficientlylarge cell gap. Those phases are therefore also called “blue phases”(Gray and Goodby, “Smectic Liquid Crystals, Textures and Structures”,Leonhard Hill, USA, Canada (1984)). Effects of electrical fields onliquid crystals existing in a blue phase are described for instance inH. S. Kitzerow, “The Effect of Electric Fields on Blue Phases”, Mol.Cryst. Liq. Cryst. (1991), Vol. 202, p. 51-83, as well as the threetypes of blue phases identified so far, namely BP I, BP II, and BP III,that may be observed in field-free liquid crystals. It is noteworthy,that if the liquid crystal exhibiting a blue phase or blue phases issubjected to an electrical field, further blue phases or other phasesdifferent from the blue phases I, II and III might appear.

The inventive mixtures can be used in an electro-opticallight-controlling element which comprises

-   -   one or more, especially two substrates;    -   an assembly of electrodes;    -   one or more elements for polarizing the light; and    -   said controlling medium;        whereby said light-controlling element is operated (or operable)        at a temperature at which the controlling medium is in an        optically isotropic phase when it is in a non-driven state.

The controlling medium of the present invention has a characteristictemperature, preferably a clearing point, in the range from about −30°C. to about 90° C., especially up to about 70° C. to 80° C.

The operating temperature of the light controlling elements ispreferably above the characteristic temperature of the controllingmedium said temperature being usually the transition temperature of thecontrolling medium to the blue phase; generally the operatingtemperature is in the range of about 0.1° to about 50°, preferably inthe range of about 0.1° to about 10° above said characteristictemperature. It is highly preferred that the operating temperature is inthe range from the transition temperature of the controlling medium tothe blue phase up to the transition temperature of the controllingmedium to the isotropic phase which is the clearing point. The lightcontrolling elements, however, may also be operated at temperatures atwhich the controlling medium is in the isotropic phase.

For the purposes of the present invention the term “characteristictemperature” is defined as follows:

-   -   If the characteristic voltage as a function of temperature has a        minimum, the temperature at this minimum is denoted as        characteristic temperature.    -   If the characteristic voltage as a function of temperature has        no minimum and if the controlling medium has one or more blue        phases, the transition temperature to the blue phase is denoted        as characteristic temperature; in case there are more than one        blue phase, the lowest transition temperature to a blue phase is        denoted as characteristic temperature.    -   If the characteristic voltage as a function of temperature has        no minimum, and if the controlling medium has no blue phase, the        transition temperature to the isotropic phase is denoted as        characteristic temperature.

In the context of the present invention the term “alkyl” means, as longas it is not defined in a different manner elsewhere in this descriptionor in the claims, straight-chain and branched hydrocarbon (aliphatic)radicals with 1 to 15 carbon atoms. The hydrocarbon radicals may beunsubstituted or substituted with one or more substituents beingindependently selected from the group consisting of F, Cl, Br, I or CN.

The dielectrics may also comprise further additives known to the personskilled in the art and described in the literature. For example, 0 to 5%of pleochroic dyes, antioxidants or stabilizers can be added.

C denotes a crystalline phase, S a smectic phase, S_(C) a smectic Cphase, N a nematic phase, I the isotropic phase and BP the blue phase.

V_(X) denotes the voltage for X % transmission. Thus e.g. V₁₀ denotesthe voltage for 10% transmission and V₁₀₀ denotes the voltage for 100%transmission (viewing angle perpendicular to the plate surface). t_(on)(respectively τ_(on)) denotes the switch-on time and t_(off)(respectively τ_(off)) the switch-off time at an operating voltagecorresponding the value of V₁₀₀, respectively of V_(max). t_(on) is thetime for the change of the relative transmission from 10% to 90% andt_(off) is the time for the change of the relative transmission from 90%to 10%. The response times are determined with the measurementinstrument DMS from Autronic Melchers, Germany, just as theelectro-optical characteristics.

Δn denotes the optical anisotropy. Δ∈ denotes the dielectric anisotropy(Δ∈=∈_(∥)−∈_(⊥), where ∈_(∥) denotes the dielectric constant parallel tothe longitudinal molecular axes and ∈_(⊥) denotes the dielectricconstant perpendicular thereto). The electro-optical data are measuredin a TN cell at the 1^(st) minimum of transmission (i.e. at a (d·Δn)value of 0.5 μm) at 20° C., unless expressly stated otherwise. Theoptical data are measured at 20° C., unless expressly stated otherwise.

Optionally, the light modulation media according to the presentinvention can comprise further liquid crystal compounds in order toadjust the physical properties. Such compounds are known to the expert.Their concentration in the media according to the instant invention ispreferably 0% to 30%, more preferably 0% to 20% and most preferably 5%to 15%.

Preferably inventive media have a range of the blue phase or, in case ofthe occurrence of more than one blue phase, a combined range of the bluephases, with a width of 20° or more, preferably of 40° or more, morepreferably of 50° or more and most preferably of 60° or more.

In a preferred embodiment this phase range is at least from 10° C. to30° C., most preferably at least from 10° C. to 40° C. and mostpreferably at least from 0° C. to 50° C., wherein at least means, thatpreferably the phase extends to temperatures below the lower limit andat the same time, that it extends to temperatures above the upper limit.

In another preferred embodiment this phase range is at least from 20° C.to 40° C., most preferably at least from 30° C. to 80° C. and mostpreferably at least from 30° C. to 90° C. This embodiment isparticularly suited for displays with a strong backlight, dissipatingenergy and thus heating the display.

Preferably the inventive media have a dielectric anisotropy of 150 ormore, more preferably of 200 or more, even more preferably of 300 ormore and most preferably of 400 or more. In particular, the value ofdielectric anisotropy of the inventive media is preferably 700 or less,more preferably 550 or less and, most preferably 500 or less.

In the present application the term dielectrically positive compoundsdescribes compounds with Δ∈>1.5, dielectrically neutral compounds arecompounds with −1.5≦Δ∈≦1.5 and dielectrically negative compounds arecompounds with Δ∈<−1.5. The same holds for components. Δ∈ is determinedat 1 kHz and 20° C. The dielectric anisotropies of the compounds isdetermined from the results of a solution of 10% of the individualcompounds in a nematic host mixture. The capacities of these testmixtures are determined both in a cell with homeotropic and withhomogeneous alignment. The cell gap of both types of cells isapproximately 20 μm. The voltage applied is a rectangular wave with afrequency of 1 kHz and a root mean square value typically of 0.5 V to1.0 V, however, it is always selected to be below the capacitivethreshold of the respective test mixture.

For dielectrically positive compounds the mixture ZLI-4792 and fordielectrically neutral, as well as for dielectrically negativecompounds, the mixture ZLI-3086, both of Merck KGaA, Germany are used ashost mixture, respectively. The dielectric permittivities of thecompounds are determined from the change of the respective values of thehost mixture upon addition of the compounds of interest and areextrapolated to a concentration of the compounds of interest of 100%.

Components having a nematic phase at the measurement temperature of 20°C. are measured as such, all others are treated like compounds.

The term threshold voltage refers in the instant application to theoptical threshold and is given for 10% relative contrast (V₁₀) and theterm saturation voltage refers to the optical saturation and is givenfor 90 relative contrast (V₉₀) both, if not explicitly stated otherwise.The capacitive threshold voltage (V₀, also called Freedericksz-thresholdV_(Fr)) is only used if explicitly mentioned.

The ranges of parameters given in this application are all including thelimiting values, unless explicitly stated otherwise.

Throughout this application, unless explicitly stated otherwise, allconcentrations are given in mass percent and relate to the respectivecomplete mixture, all temperatures are given in degrees centigrade(Celsius) and all differences of temperatures in degrees centigrade. Allphysical properties have been and are determined according to “MerckLiquid Crystals, Physical Properties of Liquid Crystals”, StatusNovember 1997, Merck KGaA, Germany and are given for a temperature of20° C., unless explicitly stated otherwise. The optical anisotropy (Δn)is determined at a wavelength of 589.3 nm. The dielectric anisotropy(Δ∈) is determined at a frequency of 1 kHz. The threshold voltages, aswell as all other electro-optical properties have been determined withtest cells prepared at Merck KGaA, Germany. The test cells for thedetermination of Δ∈ had a cell gap of 22 μm. The electrode was acircular ITO electrode with an area of 1.13 cm² and a guard ring. Theorientation layers were lecithin for homeotropic orientation (∈∥) andpolyimide AL-1054 from Japan Synthetic Rubber for homogenous orientation(∈⊥). The capacities were determined with a frequency response analyserSolatron 1260 using a sine wave with a voltage of 0.3 or 0.1 V_(rms).The light used in the electro-optical measurements was white light. Theset up used was a commercially available equipment of Otsuka, Japan. Thecharacteristic voltages have been determined under perpendicularobservation. The threshold voltage (V₁₀), mid-grey voltage (V₅₀) andsaturation voltage (V₉₀) have been determined for 10%, 50% and 90%relative contrast, respectively.

The mesogenic modulation material has been filled into an electrooptical test cell prepared at the respective facility of Merck KGaA. Thetest cells had inter-digital electrodes on one substrate side. Theelectrode width was 10 μm, the distance between adjacent electrodes was10 μm and the cell gap was also 10 μm. This test cell has been evaluatedelectro-optically between crossed polarisers.

At low temperatures, the filled cells showed the typical texture of achiral nematic mixture, with an optical transmission between crossedpolarisers without applied voltage. Upon heating, at a first temperature(T₁) the mixtures turned optically isotropic, being dark between thecrossed polarisers. This indicated the transition from the chiralnematic phase to the blue phase at that temperature. Up to a secondtemperature (T₂) the cell showed an electro-optical effect under appliedvoltage, typically of some tens of volts, a certain voltage in thatrange leading to a maximum of the optical transmission. Typically at ahigher temperature the voltage needed for a visible electro-opticaleffect increased strongly, indicating the transition from the blue phaseto the isotropic phase at this second temperature (T₂).

The temperature range (ΔT(BP)), where the mixture can be usedelectro-optically in the blue phase most beneficially has beenidentified as ranging from T₁ to T₂. This temperature range (ΔT(BP)) isthe temperature range given in the examples of this application. Theelectro-optical displays can also be operated at temperatures beyondthis range, i.e. at temperatures above T₂, albeit only at significantlyincreased operation voltages.

The liquid crystal media according to the present invention can containfurther additives and chiral dopants in usual concentrations. The totalconcentration of these further constituents is in the range of 0% to10%, preferably 0.1% to 6%, based in the total mixture. Theconcentrations of the individual compounds used each are preferably inthe range of 0.1 to 3%. The concentration of these and of similaradditives is not taken into consideration for the values and ranges ofthe concentrations of the liquid crystal components and compounds of theliquid crystal media in this application.

The inventive liquid crystal media according to the present inventionconsist of several compounds, preferably of 3 to 30, more preferably of5 to 20 and most preferably of 6 to 14 compounds. These compounds aremixed in conventional way. As a rule, the required amount of thecompound used in the smaller amount is dissolved in the compound used inthe greater amount. In case the temperature is above the clearing pointof the compound used in the higher concentration, it is particularlyeasy to observe completion of the process of dissolution. It is,however, also possible to prepare the media by other conventional ways,e.g. using so called pre-mixtures, which can be e. g. homologous oreutectic mixtures of compounds or using so called multi-bottle-systems,the constituents of which are ready to use mixtures themselves.

By addition of suitable additives, the liquid crystal media according tothe instant invention can be modified in such a way, that they areusable in all known types of liquid crystal displays, either using theliquid crystal media as such, like TN-, TN-AMD, ECB-, VAN-AMD(vertically aligned nematic-active matrix display) and in particular incomposite systems, like PDLC-(polymer dispersed liquid crystal), NCAP-(nematically curvilinerarily aligned polymer) and PN- (polymer network)LCDs and especially in HPDLCs (holographic PDLCs).

The melting point: T(K,N), T(K,S) or T(K,I), respectively, thetransition temperature from one smectic phase (S_(X)) to another smecticphase (S_(Y)): T(S_(X),S_(Y)), the transition temperature from thesmectic (S) to the nematic (N) phase: T(S,N), the clearing point: T(N,I), and the glass transition temperature: T_(g) of the liquidcrystals, as applicable, as well as any other temperature throughoutthis application, are given in degrees centi-grade (i.e. Celsius).

The compounds of the formula P and the sub-formulae thereof can beprepared analogously to the process known to the person skilled in theart and described in standard works of organic chemistry, such as, forexample, in Houben-Weyl, Methoden der organischen Chemie [Methods ofOrganic Chemistry], Thieme-Verlag, Stuttgart.

Particularly suitable and preferred processes for the preparation ofcompounds of the formula P and the sub-formulae thereof are shown by wayof example in the following schemes and preferably comprise one or moreof the steps described below.

The person skilled in the art will be able to modify the synthesis in asuitable manner and thus obtain further compounds according to theinvention. The particularly preferred compounds containing an alkoxyspacer or acrylates bonded directly to the ring are obtained, forexample, by reaction of phenol derivatives, such as, for example,compound 12, with the dithianylium salts 13. The compounds 14 formedinitially here are converted into the compounds 15. The hydroxyl groupcan subsequently be functionalised in a suitable manner, for example byesterification using methacrylic acid (cf. Scheme 1).

The compounds of formula P wherein the rings are linked by an —CF₂—O—group and the reactive groups are attached to the rings via an alkylenespacer group, which are used according to the present invention in aparticularly preferred embodiment, can be prepared according to thefollowing scheme.

In the present invention and especially in the following examples, thestructures of the mesogenic compounds are indicated by means ofabbreviations, also called acronyms. In these acronyms, the chemicalformulae are abbreviated as follows using Tables A to C below. Allgroups C_(n)H_(2n+1), C_(m)H_(2m+1) and C_(l)H_(2l+1) or C_(n)H_(2n−1),C_(m)H_(2m−1) and C_(l)H_(2l−1) denote straight-chain alkyl or alkenyl,preferably 1E-alkenyl, each having n, m and l C atoms respectively.Table A lists the codes used for the ring elements of the corestructures of the compounds, while Table B shows the linking groups.Table C gives the meanings of the codes for the left-hand or right-handend groups. The acronyms are composed of the codes for the ring elementswith optional linking groups, followed by a first hyphen and the codesfor the left-hand end group, and a second hyphen and the codes for theright-hand end group. Table D shows illustrative structures of compoundstogether with their respective abbreviations.

TABLE A Ring elements C

P

D

DI

A

AI

G

GI

U

UI

Y

M

MI

N

NI

Np

dH

N3f

N3fI

tH

tHI

tH2F

tH2fI

K

KI

L

LI

F

FI

TABLE B Linking groups E —CH₂CH₂— Z —CO—O— V —CH═CH— ZI —O—CO— X —CF═CH—O —CH₂—O— XI —CH═CF— OI —O—CH₂— B —CF═CF— Q —CF₂—O— T —C≡C— QI —O—CF₂— W—CF₂CF₂— T —C≡C—

TABLE C End groups Left-hand side Right-hand side Use alone -n-C_(n)H_(2n+1)— -n —C_(n)H_(2n+1) -nO- C_(n)H_(2n+1)—O— -nO—O—C_(n)H_(2n+1) -V- CH₂═CH— -V —CH═CH₂ -nV- C_(n)H_(2n+1)—CH═CH— -nV—C_(n)H_(2n)—CH═CH₂ -Vn- CH₂═CH—C_(n)H_(2n+1)— -Vn —CH═CH—C_(n)H_(2n+1)-nVm- C_(n)H_(2n+1)—CH═CH—C_(m)H_(2m)— -nVm—C_(n)H_(2n)—CH═CH—C_(m)H_(2m+1) -N- N≡C— -N —C≡N -S- S═C═N— -S —N═C═S-F- F— -F —F -CL- Cl— -CL —Cl -M- CFH₂— -M —CFH₂ -D- CF₂H— -D —CF₂H -T-CF₃— -T —CF₃ -MO- CFH₂O— -OM —OCFH₂ -DO- CF₂HO— -OD —OCF₂H -TO- CF₃O—-OT —OCF₃ -FXO- CF₂═CH—O— -OXF —O—CH═CF₂ -A- H-C≡C— -A —C≡C—H -nA-C_(n)H_(2n+1)—C≡C— -An —C≡C—C_(n)H_(2n+1) -NA- N≡C—C≡C— -AN —C≡C—C≡N Usetogether with one another and/or with others -...A...- —C≡C— -...A...—C≡C— -...V...- CH═CH— -...V... —CH═CH— -...Z...- —CO—O— -...Z... —CO—O—-...ZI...- —O—CO— -...ZI... —O—CO— -...K...- —CO— -...K... —CO—-...W...- —CF═CF— -...W... —CF═CF—in which n and m each denote integers, and the three dots “ . . . ” areplaceholders for other abbreviations from this table.

The following table shows illustrative structures together with theirrespective abbreviations. These are shown in order to illustrate themeaning of the rules for the abbreviations. They furthermore representcompounds which are preferably used.

TABLE D Illustrative structures

in which n (and also m and l) preferably, independently of one another,denote(s) an integer from 1 to 7, preferably from 2 to 6.

The following table, Table E, shows illustrative compounds which can beused as stabiliser in the mesogenic media according to the presentinvention.

TABLE E

In a preferred embodiment of the present invention, the mesogenic mediacomprise one or more compounds selected from the group of the compoundsfrom Table E.

The following table, Table F, shows illustrative compounds which canpreferably be used as chiral dopants in the mesogenic media according tothe present invention.

TABLE F

In a preferred embodiment of the present invention, the mesogenic mediacomprise one or more compounds selected from the group of the compoundsfrom Table F.

The mesogenic media according to the present application preferablycomprise two or more, preferably four or more, compounds selected fromthe group consisting of the compounds from the above tables. Theliquid-crystal media according to the present invention preferablycomprise

-   -   seven or more, preferably eight or more, compounds, preferably        compounds having three or more, preferably four or more,        different formulae, selected from the group of the compounds        from Table D.

EXAMPLES

The examples below illustrate the present invention without limiting itin any way.

However, the physical properties show the person skilled in the art whatproperties can be achieved and in what ranges they can be modified. Inparticular, the combination of the various properties which canpreferably be achieved is thus well defined for the person skilled inthe art.

Liquid-crystal mixtures having the composition and properties asindicated in the following tables are prepared and investigated.

The so-called “HTP” denotes the helical twisting power of an opticallyactive or chiral substance in an LC medium (in μm⁻¹). Unless indicatedotherwise, the HTP is measured in the commercially available nematic LChost mixture MLD-6260 (Merck KGaA) at a temperature of 20° C.

Synthesis Example 16-(4-{[4-(6-Acryloyloxyhexyl)phenoxy]-difluoromethyl}-3,5-difluorophenyl)hexylacrylate 1.1:5-Bromo-2[(4-bromophenoxy)difluoromethyl]-1,3-difluorobenzene

92.0 g (0.200 mol) of2-(4-bromo-2,6-difluorophenyl)-5,6-dihydro-4H-1,3-dithiyn-1-yliumtriflate are initially introduced in 600 ml of dichloromethane, and asolution of 52.0 g (0.300 mol) of 4-bromophenol in 200 ml ofdichloromethane and 45 ml of triethylamine is added at −70° C. When theaddition is complete, the mixture is stirred at −70° C. for a further 1h, 160 ml (1.00 mol) of triethylamine trishydrofluoride are added, and asolution of 51.0 ml (0.996 mol) of bromine in 200 ml of dichloromethaneis subsequently added dropwise. After 1 h, the cooling is removed, and,after warming to −10° C., the batch is added to a solution of 310 ml of32 per cent sodium hydroxide solution in 2 l of ice-water. The org.phase is separated off and washed with water. The aqueous phase isextracted with dichloromethane, and the combined org. phases are driedover sodium sulfate. The solvent is removed in vacuo, and the residue isfiltered through silica gel with heptane, giving5-bromo-2-[(4-bromophenoxy)-difluoromethyl]-1,3-difluorobenzene as ayellow oil.

-   ¹⁹F-NMR (CDCl₃, 235 MHz)-   δ=−63.1 ppm (t, J=26.7 Hz, 2F, —CF₂O—), −112 (dt, J=9.7 Hz,-   J=26.7 Hz, 2F, Ar—F).

1.2:6-(4-{Difluoro[4-(6-hydroxyhex-1-ynyl)phenoxy]methyl}-3,5-difluorophenyl)hex-5-yn-1-ol

10.7 g (25.8 mmol) of5-bromo-2-[(4-bromophenoxy)difluoromethyl]-1,3-difluorobenzene and 8.00g (81.5 mmol) of hex-5-yn-1-ol are initially introduced in 11.3 ml oftriethylamine and 500 ml of toluene, 1.50 g (2 mmol) ofbis(triphenylphosphine)palladium(II) chloride and 0.700 g (3.68 mmol) ofcopper(I) iodide are added, and the mixture is heated under refluxovernight. The batch is subsequently added to water, neutralised using 2N hydrochloric acid and extracted three times with toluene. The combinedorg. phases are dried over sodium sulfate, the solvent is removed invacuo, and the residue is chromatographed on silica gel firstly withtoluene and then with toluene/ethyl acetate (4:1), giving6-(4-{difluoro[4-(6-hydroxyhex-1-ynyl)phenoxy]methyl}-3,5-difluorophenyl)hex-5-yn-1-olas a colourless solid.

1.3:6-(4-{Difluoro[4-(6-hydroxyhexyl)phenoxy]methyl}-3,5-difluorophenyl)hexan-1-ol

6-(4-{Difluoro[4-(6-hydroxyhex-1-ynyl)phenoxy]methyl}-3,5-difluorophenyl)-hex-5-yn-1-olis hydrogenated to completion on palladium/active carbon catalyst inTHF. The catalyst is filtered off, the solvent is removed in vacuo, andthe crude product is chromatographed on silica gel with toluene/ethylacetate (1:2), giving6-(4-{difluoro[4-(6-hydroxyhexyl)-phenoxy]methyl}-3,5-difluorophenyl)hexan-1-olas a colourless solid.

-   ¹⁹F-NMR (CDCl₃, 235 MHz)-   δ=−60.8 ppm (t, J=26.3 Hz, 2F, —CF₂O—), −112 (dt, J=10.0 Hz,-   J=26.3 Hz, 2F, Ar—F).

1.4:6-(4-{[4-(6-Acryloyloxyhexyl)phenoxy]difluoromethyl}-3,5-difluoro-phenyl)hexylacrylate

17.0 g (37.2 mmol) of6-(4-{difluoro[4-(6-hydroxyhexyl)phenoxy]methyl}-3,5-difluorophenyl)hexan-1-01,8.05 g (112 mmol) of acrylic acid and 0.5 g of DMAP are initiallyintroduced in 300 ml of dichloromethane, and a solution of 17.3 g (112mmol) of EDC in 75 ml of dichloromethane is added dropwise with icecooling. After 1 h, the cooling is removed, and the batch is left tostir overnight at room temp. The vast majority of the solvent is removedin vacuo, and the residue is chromatographed on silica gel withdichloromethane, giving6-(4-{[4-(6-acryloyloxyhexyl)phenoxy]difluoromethyl}-3,5-difluorophenyl)hexylacrylate as a colourless oil.

Phase behaviour: T_(g) −71° C. K 13 l.

-   ¹H-NMR (CDCl₃, 250 MHz)-   δ=1.25-1.48 ppm (m, 8H, CH₂), 1.50-1.74 ppm (m, 8H, CH₂), 2.60 (m,    4H, 2-Ar—CH₂—), 4.13 (t, J=6.7 Hz, 2H, —CH₂O—), 4.15 (t, J=6.7 Hz,    2H, —CH₂O—), 5.81 (dt, J=10.4 Hz, J=1.8 Hz, 2H, 2 CHH═CH—COO—), 6.11    (m_(c), 2 H, 2 CH₂═CH—COO—), 6.39 (2 CHH═CH—COO—), 6.78 (d, J=10.0    Hz, 2H, Ar—H), 7.15 (m_(c), 4 H, Ar—H).-   ¹⁹F-NMR (CDCl₃, 235 MHz)-   δ=−60.9 ppm (t, J=26.4 Hz, 2F, —CF₂O—), −112.0 (dt, J=26.4, J=10.0    Hz, 2F, Ar—F).

Analogously the following reactive compounds are obtained

Phase behaviour: to be determined.

Phase behaviour: T_(g) −66° C. I.

Phase behaviour: T_(g) −69° C. I.

Phase behaviour: to be determined.

Phase behaviour: to be determined.

Phase behaviour: to be determined.

Phase behaviour: to be determined.

Phase behaviour: C 128° C. I.

Phase behaviour: T_(g) −59° C. N −28.5° C. I.

The entire disclosures of all applications, patents and publications,cited herein and of corresponding application No. 12006552.9 EP, filedSep. 18, 2012 are incorporated by reference herein.

Example 1

The following liquid crystalline mixture M-1 is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture M-1 CompositionCompound Conc./ No. Abbreviation mass-% 1 UM-3-N 10.0 2 PZG-3-N 8.0 3GUQU-3-N 8.0 4 GUUQU-3-N 15.0 5 PUQGU-3-T 10.0 6 PUQGU-5-T 10.0 7DUUQU-3-F 10.0 8 DUUQU-4-F 12.0 9 DUUQU-5-F 12.0 10  PPGU-3-F 5.0 Σ100.0 Physical Properties T (N, I) = 72° C. n_(o) (20° C., 589 nm) =t.b.d. Δn (20° C., 589 nm) = t.b.d. ε_(⊥) (20°, 1 kHz) = t.b.d. Δε (20°,1 kHz) = t.b.d. γ₁ (20° C.) = t.b.d. mP · s Remark: t.b.d.: to bedetermined

3.8% of the chiral agent R-5011 are solved in the achiral liquid crystalmixture and the electro-optical response of resultant mixture in anIPS-type cell is investigated. The mixture is filled into an electrooptical test cell with inter-digital electrodes on one substrate side.The electrode width is 10 μm, the distance between adjacent electrodesis 10 μm and the cell gap is also 10 μm. This test cell is evaluatedelectro-optically between crossed polarisers.

Appropriate concentrations

-   a) of the chiral dopant R-5011 (Merck KGaA, Germany),-   b) of the reactive mesogen of the formula RM-C

and

-   c) alternatively of one of the two reactive mesogenic compounds of    the formulae RM-1

and RM-2

respectively, are added to the mixture of interest, here mixture M-1.The resultant mixture is introduced into test cells and heated to anappropriate temperature, at which the mixture is in the blue phase. Thenit is exposed to UV.

The mixtures are characterised as described below before thepolymerisation. The reactive components are then polymerised in the bluephase by irradiation once (180 s), and the resultant media arerecharacterised.

Detailed Description of the Polymerisation

Before the polymerisation of a sample, the phase properties of themedium are established in a test cell having a thickness of about 10microns and an area of 2×2.5 cm². The filling is carried out bycapillary action at a temperature of 75° C. The measurement is carriedout under a polarising microscope with heating stage with a temperaturechange of 1° C./min.

The polymerisation of the media is carried out by irradiation with a UVlamp (Dymax, Bluewave 200, 365 nm interference filter) having aneffective power of about 3.0 mW/cm² for 180 seconds. The polymerisationis carried out directly in the electro-optical test cell.

The polymerisation is carried out initially at a temperature at whichthe medium is in the blue phase I (BP-I). The polymerisation is carriedout in a plurality of part-steps, which gradually result in completepolymerisation. The temperature range of the blue phase generallychanges during the polymerisation. The temperature is therefore adaptedbetween each part-step so that the medium is still in the blue phase. Inpractice, this can be carried out by observing the sample under thepolarising microscope after each irradiation operation of about 5 s orlonger. If the sample becomes darker, this indicates a transition intothe isotropic phase. The temperature for the next part-step is reducedcorrespondingly.

The entire irradiation time which results in maximum stabilisation istypically 180 s at the irradiation power indicated. Furtherpolymerisations can be carried out in accordance with an optimisedirradiation/temperature programme.

Alternatively, the polymerisation can also be carried out in a singleirradiation step, in particular if a broad blue phase is already presentbefore the polymerisation.

Electro-Optical Characterisation

After the above-described polymerisation and stabilisation of the bluephase, the phase width of the blue phase is determined. Theelectro-optical characterisation is carried out subsequently at varioustemperatures within and if desired also outside this range.

The test cells used are fitted on one side with interdigital electrodeson the cell surface. The cell gap, the electrode separation and theelectrode width are typically each 10 microns. This uniform dimension isreferred to below as the gap width. The area covered by electrodes isabout 0.4 cm². The test cells do not have an alignment layer.

For the electro-optical characterisation, the cell is located betweencrossed polarising filters, where the longitudinal direction of theelectrodes adopts an angle of 45° to the axes of the polarising filter.The measurement is carried out using a DMS301 (Autronic-Melchers,Germany) at a right angle to the cell plane, or by means of a highlysensitive camera on the polarising microscope. In the voltage-freestate, the arrangement described gives an essentially dark image(definition 0% transmission).

Firstly, the characteristic operating voltages and then the responsetimes are measured on the test cell. The operating voltage is applied tothe cell electrodes in the form of rectangular voltage having analternating sign (frequency 100 Hz) and variable amplitude, as describedbelow.

The transmission is measured while the operating voltage is increased.The attainment of the maximum value of the transmission defines thecharacteristic quantity of the operating voltage V₁₀₀. Equally, thecharacteristic voltage V₁₀ is determined at 10% of the maximumtransmission. These values are measured at various temperatures in therange of the blue phase.

Relatively high characteristic operating voltages V₁₀₀ are observed atthe upper and lower end of the temperature range of the blue phase. Inthe region of the minimum operating voltage, V₁₀₀ generally onlyincreases slightly with increasing temperature. This temperature range,limited by T₁ and T₂, is referred to as the usable, flat temperaturerange (FR). The width of this “flat range” (FR) is (T₂-T₁) and is knownas the width of the flat range (WFR). The precise values of T₁ and T₂are determined by the intersections of tangents on the flat curvesection FR and the adjacent steep curve sections in the V₁₀₀/temperaturediagram.

In the second part of the measurement, the response times (τ) forswitching on and off (τ_(off), τ_(off)) are determined. The responsetime τ_(on) is defined by the time to achievement of 90% intensity afterapplication of a voltage at the level of V₁₀₀ at the selectedtemperature. The response time τ_(off) is defined by the time until thedecrease by 90% starting from maximum intensity at V₁₀₀ after reductionof the voltage to 0 V. The response time is also determined at varioustemperatures in the range of the blue phase.

As further characterisation, the transmission at continuously increasingand falling operating voltage between 0 V and V₁₀₀ is measured at atemperature within the FR. The difference between the two curves isknown as hysteresis. The difference in the transmissions at 0.5·V₁₀₀ andthe difference in the voltages at 50% transmission are, for example,characteristic hysteresis values and are known as ΔT₅₀ and ΔV₅₀respectively.

As a further characteristic quantity, the ratio of the transmission inthe voltage-free state before and after passing through a switchingcycle can be measured. This transmission ratio is referred to as the“memory effect”. The value of the memory effect is 1.0 in the idealstate. Values above 1 mean that a certain memory effect is present inthe form of excessively high residual transmission after the cell hasbeen switched on and off. This value is also determined in the workingrange of the blue phase (FR).

Typical concentrations of the polymer precursors are as follows.

Sample 1.1 1.2 1.3 Constituent Concentration/% M-1 88.0 89.0 87.4 R-50113.8 3.8 3.4 RM-C 5.0 4.0 5.0 RM-2 4.0 3.0 4.0 IRG-651 ® 0.2 0.2 0.2 Σ100.0 100.0 100.0

The results are summarised in the following table.

Mixture M-1-1 M-1-2 M-1-3 Host M-1 M-1 M-1 Reactive mesogen RM-2 RM-2RM-2 Transition point before the polymerisation t.b.d. t.b.d. t.b.d.Polymerisation temperature/° C. t.b.d. t.b.d. t.b.d. V₁₀ (20° C.)/Vt.b.d. t.b.d. t.b.d. V₅₀ (20° C.)/V t.b.d. t.b.d. t.b.d. V₉₀ (20° C.)/Vt.b.d. t.b.d. t.b.d. V₁₀₀ (20° C.)/V t.b.d. t.b.d. t.b.d. ΔV₅₀ (20°C.)/V t.b.d. t.b.d. t.b.d. Contrast (20° C.), switching on t.b.d. t.b.d.t.b.d. Contrast (20° C.), switching off t.b.d. t.b.d. t.b.d. Memoryeffect (20° C.) t.b.d. t.b.d. t.b.d. τ_(on) (20° C.)/ms t.b.d. t.b.d.t.b.d. τ_(off) (20° C.)/ms t.b.d. t.b.d. t.b.d. Remarks: t.b.d.: to bedetermined

The polymerisable mixture is polymerised in a single irradiation step ata temperature of about 30-50° C. at the lower end of the temperaturerange of the blue phase. The polymer-stabilised liquid-crystalline mediaexhibit a blue phase over a broad temperature range.

The polymer-stabilised medium M-1, prepared using the monomer (1)according to the invention, exhibits a reduction in hysteresis (ΔV₅₀)and good contrast on switching on and on switching off compared withconventional media from the prior art. In particular, the contrast onswitching on and the contrast on switching off are close together in themedium M-1 according to the invention, which means very goodstabilisation of the blue phase.

It can be seen from this that the monomers according to the inventionare particularly suitable for the stabilisation of blue phases, inparticular in the case of media having a high concentration of chiraldopant.

Comparative Examples 1-1 and 1-2

The following liquid crystalline mixture (C-1) is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture C-1 CompositionCompound Conc./ No. Abbreviation mass-% 1 AUUQU-2-F 10.0 2 AUUQU-3-F11.0 3 AUUQU-4-F 7.0 4 AUUQU-5-F 6.0 5 AUUQU-7-F 7.0 6 AUUQU-3-T 10.0 7AUUQU-3-OT 11.0 8 AGUQU-3-F 4.0 9 AUUQU-3-N 5.0 10  PUZU-2-F 7.0 11 PUZU-3-F 11.0 12  PUZU-5-F 11.0 Σ 100.0 Physical Properties T (N, I) =71° C. n_(o) (20° C., 589 nm) = 1.4812 Δn (20° C., 589 nm) = 0.1543ε_(⊥) (20°, 1 kHz) = 14.8 Δε (20°, 1 kHz) = 212 γ₁ (30° C.) = 763 mP · s

This mixture is treated and investigated as described in detail underexample 1 above.

The results are compiled in the following table.

Mixture C-1-1 C-1-2 Host C-1 Reactive mesogen RM-1 RM-2 Transition pointbefore the polymerisation t.b.d. t.b.d. Polymerisation temperature/° C.t.b.d. t.b.d. V₁₀ (20° C.)/V 29.8 20.8 V₅₀ (20° C.)/V t.b.d. t.b.d. V₉₀(20° C.)/V 58.6 42.0 V₁₀₀ (20° C.)/V 67.0 47.9 ΔV₅₀ (20° C.)/V 4.73 1.90Contrast (20° C.), switching on 285 206 Contrast (20° C.), switching off276 208 Memory effect (20° C.) 1.04 0.99 τ_(on) (20° C.)/ms t.b.d.t.b.d. τ_(off) (20° C.)/ms t.b.d. t.b.d. Remarks: t.b.d.: to bedetermined

Comparative Example 2

The following liquid crystalline mixture (C-2) is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture C-2 CompositionCompound Conc./ No. Abbreviation mass-% 1 GUQU-3-F 5.0 2 GUQU-4-F 6.0 3GUQU-5-F 6.0 4 PUQGU-3-T 8.0 5 PUQGU-5-T 8.0 6 GUQGU-2-T 12.0 7GUQGU-3-T 12.0 8 GUQGU-4-T 14.0 9 GUQGU-5-T 14.0 10  GUQU-3-N 5.0 11 GUUQU-3-N 10.0 Σ 100.0 Physical Properties T (N, I) = 65° C. n_(o) (20°C., 589 nm) = 1.4831 Δn (20° C., 589 nm) = 0.1859 ε _(⊥)20°, 1 kHz) =12.9 Δε (20°, 1 kHz) = 277.8 Mixture CM-2-1 CM-2-2 Host C-2 Reactivemesogen RM-1 RM-2 Measurement values (20° C.) Transition point beforethe polymerisation t.b.d. t.b.d. Polymerisation temperature/° C. t.b.d.t.b.d. V₁₀ (20° C.)/V t.b.d. 19.5 V₅₀ (20° C.)/V t.b.d. t.b.d. V₉₀ (20°C.)/V t.b.d. 38.2 V₁₀₀ (20° C.)/V t.b.d. 43.0 ΔV₅₀ (20° C.)/V t.b.d.2.16 Contrast (20° C.), switching on t.b.d. t.b.d. Contrast (20° C.),switching off t.b.d. t.b.d. Memory effect (20° C.) t.b.d. 1.03 τ_(on)(20° C.)/ms t.b.d. t.b.d. τ_(off) (20° C.)/ms t.b.d. t.b.d. V₁₀₀ (30°C.)/V t.b.d. 52.0 Contrast (30° C.), switching on t.b.d. 159.5 Contrast(30° C.), switching off t.b.d. 144.4 Memory effect (30° C.) t.b.d. 1.10τ_(on) (30° C.)/ms t.b.d. t.b.d. τ_(off) (30° C.)/ms t.b.d. t.b.d.Remarks: t.b.d.: to be determined

Example 2

The following liquid crystalline mixture M-2 is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture M-2 CompositionCompound Conc./ No. Abbreviation mass-% 1 UM-3-N 10.0 2 GUQU-2-N 8.0 3GUQU-3-N 9.0 4 GUUQU-3-N 12.0 5 PUQGU-3-T 11.0 6 PUQGU-4-T 11.0 7PUQGU-5-T 10.0 8 DUUQU-4-F 12.0 9 DUUQU-5-F 12.0 10  PPGU-3-F 5.0 Σ100.0 Physical Properties T (N, I) = 70.5° C. n_(o) (20° C., 589 nm) =t.b.d. Δn (20° C., 589 nm) = t.b.d. ε_(⊥) (20°, 1 kHz) = t.b.d. Δε (20°,1 kHz) = t.b.d. γ₁ (20° C.) = t.b.d. mPa · s Remark: t.b.d.: to bedetermined

Typical concentrations of the polymer precursors are as follows.

Sample 2.1 2.2 Constituent Concentration % M-2 88 88 R-5011 3.8 3.8 RM-C5.0 5.25 RM-1 0.0 0.0 RM-2 3.0 2.75 IRG-651 ® 0.2 0.2 Σ 100.0 100.0Remark: t.b.d.: to be determined

The results are summarised in the following table.

Mixture M-2-1 M-2-2 Host M-2 M-2 Reactive mesogen Measurement values(20° C.) RM-2 RM-2 Transition point before the polymerisation t.b.d.t.b.d. Polymerisation temperature/° C. t.b.d. t.b.d. V₁₀ (20° C.)/Vt.b.d. t.b.d. V₅₀ (20° C.)/V t.b.d. t.b.d. V₉₀ (20° C.)/V t.b.d. t.b.d.V₁₀₀ (20° C.)/V t.b.d. t.b.d. ΔV₅₀ (20° C.)/V t.b.d. t.b.d. Contrast(20° C.), switching on t.b.d. t.b.d. Contrast (20° C.), switching offt.b.d. t.b.d. Memory effect (20° C.) t.b.d. t.b.d. τ_(on) (20° C.)/mst.b.d. t.b.d. τ_(off) (20° C.)/ms t.b.d. t.b.d. Remark: t.b.d.: to bedetermined

Example 3

The following liquid crystalline mixture M-3 is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture M-3 CompositionCompound Conc./ No. Abbreviation mass-% 1 UM-2-N 5.0 2 UM-3-N 10.0 3UM-4-N 10.0 4 CPZG-3-N 6.0 5 CPZG-4-N 8.0 6 GUUQU-3-N 10.0 7 PUQGU-3-T8.0 8 PUQGU-4-T 9.0 9 PUQGU-5-T 8.0 10  DUUQU-4-F 10.0 11  DUUQU-5-F10.0 12  DPGU-4-F 6.0 Σ 100.0 Physical Properties T(N, I) = 71.5° C.n_(o)(20° C., 589 nm) = t.b.d. Δn(20° C., 589 nm) = t.b.d. ε_(⊥)(20°, 1kHz) = t.b.d. Δε(20°, 1 kHz) = t.b.d. γ₁(20° C.) = t.b.d. mP · s Remark:t.b.d.: to be determined

Typical concentrations of the polymer precursors are as follows.

Sample 3.1 3.2 3.3 3.4 Constituent Concentration % M-3 83.6 83.6 83.684.6 R-5011 4.2 4.2 4.2 4.2 RM-C 7.0 6.5 6.0 6.0 RM-1 0.0 0.5 0.0 0.0RM-2 5.0 5.5 6.0 5.0 IRG-651 ® 0.2 0.2 0.2 0.2 Σ 100.0 100.0 100.0 100.0

The results are summarised in the following table.

Mixture M-3-1 M-3-2 M-3-3 M-3-4 Host M-3 M-3 M-3 M-3 Reactive mesogenRM-2 RM-2 RM-2 RM-2 Transition point 36.0 35.3 36.0 37.2 before thepolymerisation/ ° C. Polymerisation 36.5 35.8 36.5 37.7 temperature/° C.V₁₀ (30° C.)/V 25.0 21.1 18.2 19.8 V₅₀ (30° C.)/V 42.5 36.6 31.5 34.1V₉₀ (30° C.)/V 54.8 47.5 41.2 44.1 V₁₀₀ (30° C.)/V 63.0 55.0 47.0 51.0ΔV₅₀ (30° C.)/V 0.9 1.6 t.b.d. 2.0 Memory effect 0.99 0.99 1.16 1.02(30° C.) τ_(on) (30° C.)/ms 0.9 0.95 1.82 1.22 τ_(off) (30° C.)/ms 0.891.43 2.03 1.67 Remark: t.b.d.: to be determined

Example 4

The following liquid crystalline mixture M-4 is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture M-4 CompositionCompound Conc./ No. Abbreviation mass-% 1 UM-3-N 10.0 2 CPZG-3-N 8.0 3GUQU-2-N 10.0 4 GUQU-3-N 10.0 5 GUUQU-3-N 12.0 6 PUQGU-3-T 10.0 7PUQGU-4-T 10.0 8 PUQGU-5-T 10.0 9 DUUQU-4-F 10.0 10  DUUQU-5-F 10.0 Σ100.0 Physical Properties T(N, I) = 71.0° C. n_(o)(20° C., 589 nm) =t.b.d. Δn(20° C., 589 nm) = t.b.d. ε_(⊥)(20°, 1 kHz) = t.b.d. Δε(20°, 1kHz) = t.b.d. γ₁(20° C.) = t.b.d. mP · s Remark: t.b.d.: to bedetermined

Typical concentrations of the polymer precursors are as follows.

Sample 4.1 4.2 4.3 Constituent Concentration % M-4 84.6 84.6 85.6 R-5011 4.2 4.2 4.2 RM-C 6.0 6.5 6.0 RM-1 0.0 0.0 0.0 RM-2 5.0 4.5 4.0IRG-651 ® 0.2 0.2 0.2 Σ 100.0 100.0 100.0  (MDA-12: 1352 1371 1372)  Sample 4.4 4.5 4.6 4.7 Constituent Concentration % M-4 85.6 86.5 87.584.6 R-5011 4.2 4.2 4.2 4.2 RM-C 5.75 5.5 4.75 5.5 RM-1 0.0 0.0 0.0 0.0RM-2 4.25 3.5 3.25 5.5 IRG-651 ® 0.2 0.2 0.2 0.2 Σ 100.0 100.0 100.0100.0

The results are summarised in the following table.

Mixture M-4-1 M-4-2 M-4-3 Host M-4 M-4 M-4 Reactive mesogen RM-2 RM-2RM-2 Transition point 35.4 35.0 37.2 before the polymerisation/ ° C.Polymerisation 35.9 35.5 37.7 temperature/° C. V₁₀ (30° C.)/V 17.4 22.119.3 V₅₀ (30° C.)/V 27.4 34.4 30.1 V₉₀ (30° C.)/V 34.9 43.2 38.2 V₁₀₀(30° C.)/V 39.8 49.2 43.3 ΔV₅₀ (30° C.)/V 2.3 1.4 1.6 Memory effect 1.081.01 1.02 1.00 (30° C.) τ_(on) (30° C.)/ms 1.61 1.49 1.91 τ_(off) (30°C.)/ms 2.42 1.21 1.66 Remark: t.b.d.: to be determined

Mixture M-4-4 M-4-5 M-4-6 Host M-4 M-4 M-4 Reactive mesogen RM-2 RM-2RM-2 Transition point 36.7 40.0 40.0 before the polymerisation/° C.Polymerisation 37.2 40.5 40.5 temperature/° C. V₁₀ (30° C.)/V 19.5 13.48.6 V₅₀ (30° C.)/V 30.4 25.7 t.b.d. V₉₀ (30° C.)/V 38.2 34.0 23.5 V₁₀₀(30° C.)/V 43.5 38.9 28.3 ΔV₅₀ (30° C.)/V 1.9 2.4 t.b.d. Memory effect1.02 2.35 9.1 (30° C.) τ_(on) (30° C.)/ms 1.97 4.04 67 τ_(off) (30°C.)/ms 1.72 3.39 468 Remark: t.b.d.: to be determined

Mixture M-4-7 Host M-4 Reactive mesogen RM-2 Transition point before34.9 the polymerisation/° C. Polymerisation 35.4 temperature/° C. V₁₀(30° C.)/V 12.9 V₅₀ (30° C.)/V 22.6 V₉₀ (30° C.)/V 30.1 V₁₀₀ (30° C.)/V35.1 ΔV₅₀ (30° C.)/V 4.7 Memory effect (30° C.) 3.8 τ_(on) (30° C.)/mst.b.d. τ_(off) (30° C.)/ms t.b.d. Remark: t.b.d.: to be determined

Example 5

The following liquid crystalline mixture M-5 is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture M-5 CompositionCompound Conc./ No. Abbreviation mass-% 1 UM-3-N 5.0 2 PZG-3-N 12.0 3GUQU-2-N 13.0 4 GUQU-3-N 12.0 5 GUUQU-3-N 10.0 6 GUUQU-4-N 10.0 7GUQGU-2-T 7.0 8 GUQGU-3-T 8.0 9 DUUQU-3-F 3.0 10  DUUQU-4-F 6.0 11 DUUQU-5-F 6.0 12  DPGU-4-F 8.0 Σ 100.0 Physical Properties T(N, I) =68.6° C. n_(o)(20° C., 589 nm) = t.b.d. Δn(20° C., 589 nm) = t.b.d.ε_(⊥)(20°, 1 kHz) = t.b.d. Δε(20°, 1 kHz) = t.b.d. γ₁(20° C.) = t.b.d.mPa · s Remark: t.b.d.: to be determined

To this mixture (M-5) 4.2% of R-5011, 7.5% RM-C, 3.5% RM-2 and 0.2%IRG-651® are added. The resultant mixture (M-5-1) is introduced into acell and the polymer precursor is polymerized and the resultantcomposite investigated as described above. Alternatively 4.2% of R-5011,7.0% RM-C, 5.0% RM-2 and 0.2% IRG-651® respectively 4.2% of R-5011, 7.0%RM-C, 3.0% RM-2 and 0.2% IRG-651® are added to M-5. The resultantmixtures M-5-2 and M-5-3 are investigated as described for M-5-1. Theresults are shown in the following table.

Mixture M-5-1 M-5-2 M-5-3 CM-5-1 Host M-5 CM-5 Reactive mesogenMeasurement values (20° C.) RM-2 Transition point before the t.b.d.t.b.d. t.b.d. t.b.d. polymerisation Polymerisation temperature/° C.t.b.d. t.b.d. t.b.d. t.b.d. V₁₀ (20° C.)/V t.b.d. t.b.d. t.b.d. t.b.d.V₅₀ (20° C.)/V t.b.d. t.b.d. t.b.d. t.b.d. V₉₀ (20° C.)/V t.b.d. t.b.d.t.b.d. t.b.d. V₁₀₀ (20° C.)/V t.b.d. t.b.d. t.b.d. t.b.d. ΔV₅₀ (20°C.)/V t.b.d. t.b.d. t.b.d. t.b.d. Memory effect (20° C.) t.b.d. t.b.d.t.b.d. t.b.d. V₁₀₀ (25° C.)/V 23   t.b.d t.b.d. 32   τ_(on) (25° C.)/mst.b.d. t.b.d. t.b.d. t.b.d. τ_(off) (25° C.)/ms 2.7 t.b.d t.b.d. 1.3Remark: t.b.d.: to be determined

Comparative Example 5

The following exemplary comparative liquid crystalline mixture CM-5 isprepared and investigated with respect to its general physicalproperties. The composition and properties are given in the followingtable.

Composition and properties liquid crystal mixture CM-5 CompositionCompound Conc./ No. Abbreviation mass-% 1 PZG-3-N 13.0 2 PZG-3-N 11.0 3GUQU-2-N 12.0 4 GUQU-3-N 12.0 5 GUUQU-3-N 10.0 6 GUUQU-4-N 10.0 7PUQGU-3-T 11.0 8 GUQGU-2-T 6.0 9 GUQGU-3-T 7.0 10  PPGU-4-F 4.0 11 DPGU-4-F 4.0 Σ 100.0 Physical Properties T(N, I) = 65.6° C. n_(o)(20°C., 589 nm) = t.b.d. Δn(20° C., 589 nm) = t.b.d. ε_(⊥)(20°, 1 kHz) =t.b.d. Δε(20°, 1 kHz) = t.b.d. γ₁(20° C.) = t.b.d. mPa · s Remark:t.b.d.: to be determined

Also this comparative mixture (CM-5) is doped and polymer stabilized byaddition of 4.2% of R-5011, 7.5% RM-C, 3.5% RM-2 and 0.2% IRG-651®(resulting in the mixture CM-5-1) and investigated as described underexample 5. The results are also shown in the table above for comparison.

It is obvious that both the operation voltage and the response time forswitching off, which in most cases is most impartant for the performanceof devices, are both at the same time significantly improved for theexemplary mixture compared to that of the comparative example.

Example 6

The following liquid crystalline mixture M-6 is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture M-6 CompositionCompound Conc./ No. Abbreviation mass-% 1 UM-3-N 5.0 2 PGQU-2-N 15.0 3PGQU-3-N 15.0 4 PGQU-4-N 15.0 5 GUQGU-2-T 10.0 6 GUQGU-3-T 10.0 7GUQGU-4-T 10.0 8 GUQGU-5-T 10.0 9 DPGU-4-F 10.0 Σ 100.0 PhysicalProperties T(N, I) = 58.5° C. n_(o)(20° C., 589 nm) = t.b.d. Δn(20° C.,589 nm) = t.b.d. ε_(⊥)(20°, 1 kHz) = t.b.d. Δε(20°, 1 kHz) = t.b.d.γ₁(20° C.) = t.b.d. mPa · s Remark: t.b.d.: to be determined

This mixture is treated and investigated as described under example 5above. It leads to comparable good results.

Example 7

The following liquid crystalline mixture M-7 is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture M-7 CompositionCompound Conc./ No. Abbreviation mass-% 1 UM-3-N 10.0 2 GUQU-2-N 10.0 3GUQU-3-N 9.0 4 GUUQU-3-N 12.0 5 PUQGU-3-N 10.0 6 PUQGU-4-N 10.0 7PUQGU-5-N 10.0 8 DUUQU-4-F 12.0 9 DUUQU-5-F 12.0 10  PPGU-4-F 5.0 Σ100.0 Physical Properties T(N, I) = 69° C. n_(o)(20° C., 589 nm) =t.b.d. Δn(20° C., 589 nm) = t.b.d. ε_(⊥)(20°, 1 kHz) = t.b.d. Δε(20°, 1kHz) = t.b.d. γ₁(20° C.) = t.b.d. mPa · s Remark: t.b.d.: to bedetermined

This mixture is treated and investigated as described under example 5above. It leads to comparable good results.

The invention claimed is:
 1. Mesogenic medium exhibiting a blue phase,comprising at least one compound of formula I-A

wherein R¹ is alkyl with 1 to 9 C-atoms, which is straight chain orbranched, unsubstituted, mono- or poly-substituted by F, Cl or CN, andin which one or more CH₂ groups are optionally replaced, in each caseindependently from one another, by —O—, —S—, —NR⁰¹—, —SiR⁰¹R⁰²—, —CO—,—COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CY⁰¹═CY⁰²— or —C≡C— in such amanner that O and/or S atoms are not linked directly to one another, L¹¹and L¹² are, independently of each other, H or F, Y⁰¹ and Y⁰² are,independently of each other, F, Cl or CN, and alternatively one of themmay be H, and R⁰¹ and R⁰² are, independently of each other, H or alkylwith 1 to 12 C-atoms.
 2. Mesogenic medium according to claim 1, whichadditionally comprises at least one chiral dopant.
 3. Mesogenic mediumaccording to claim 1, which additionally comprises at least one compoundof formulae I-T, I-N or I-E. . .

wherein R⁰ has the meaning given for R¹ in claim 1, R¹ has the meaninggiven in claim 1, n in each occurrence independently is 0 or 1 and L⁰¹to L⁰³ and L¹ in each occurrence are independently of one another H orF.
 4. Mesogenic medium according to claim 1, which additionallycomprises at least one compound of formula II

wherein L²¹ to L²³ are, independently of each other, H or F, R² isalkyl, which is straight chain or branched, is unsubstituted, mono- orpoly-substituted by F, Cl or CN, preferably by F, and in which one ormore CH₂ groups are optionally replaced, in each case independently fromone another, by —O—, —S—, —NR⁰¹—, —SiR⁰¹R⁰²—, —CO—, —COO—, —OCO—,—OCO—O—, —S—CO—, —CO—S—, —CY⁰¹═CY⁰²— or —C≡C— in such a manner that Oand/or S atoms are not linked directly to one another, Y⁰¹ and Y⁰² are,independently of each other, F, Cl or CN, and alternatively one of themmay be H, R⁰¹ and R⁰² are, independently of each other, H or alkyl with1 to 12 C-atoms.
 5. Medium according to claim 1, which additionallycomprises at least one compound of formula III

wherein R³ has the meaning given for R¹ in claim
 1. 6. Medium accordingto claim 1, which additionally comprises at least one compound selectedfrom the group of compounds of formulae IV and V

wherein R⁴ and R⁵ are, independently of each other, alkyl, which isstraight chain or branched, preferably has 1 to 20 C-atoms, isunsubstituted, mono- or poly-substituted by F, Cl or CN, preferably byF, and in which one or more CH₂ groups are optionally replaced, in eachcase independently from one another, by —O—, —S—, —CO—, —COO—, —OCO—,—OCO—O—, —S—CO—, —CO—S— or —C≡C— in such a manner that O and/or S atomsare not linked directly to one another, L⁵ is H or F,

 is

n and m are, independently of one another, 0 or
 1. 7. Medium accordingto claim 1, which comprises a polymerizable component, which comprisesat least one polymerizable compounds.
 8. Medium according to claim 1,which additionally comprises at least one compound of formula M1

wherein the parameters have the following meanings: P¹ and P² are each,independently of one another, a polymerisable group, Sp¹ and Sp² areeach, independently of one another, a single bond or a spacer group,and, wherein alternatively also one or more of P¹-Sp¹- and P²-Sp²- maybe R^(aa), provided that at least one of P¹-Sp¹- and P²-Sp²-present inthe compound is not R^(aa), R^(aa) is H, F, Cl, CN or linear or branchedalkyl having 1 to 25 C-atoms, wherein one or more non-adjacent —CH₂—groups, independently of each another, may be replaced by—C(R⁰)═C(R⁰⁰)—, —C≡C—, —N(R⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—in such a way that neither O- nor S-atoms are directly linked to oneanother, and wherein also one or more H-atoms may be replaced by F, Cl,CN or P¹-Sp¹-, R⁰, R⁰⁰ are each, at each occurrence independently of oneanother, H or alkyl having 1 to 12 C-atoms, L is at each occurrenceindependently of one another, F, Cl, CN, SCN, SF₅ or linear or branched,optionally mono- or poly-fluorinated, alkyl, alkoxy, alkenyl, alkinyl,alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxyhaving 1 to 12 C-atoms, and r is 0, 1, 2, 3 or
 4. 9. Medium according toclaim 1, which additionally comprises at least one compound of formulaM2

wherein the parameters have the following meanings P¹ and P² are each,independently of one another, a polymerisable group, Sp¹ and Sp² areeach, independently of one another, a single bond or a spacer group,and, wherein alternatively also one or more of P¹-Sp¹- and P²-Sp²- maybe R^(aa), provided that at least one of P¹-Sp¹- and P²-Sp²-present inthe compound is not R^(aa), R^(aa) is H, F, Cl, CN or linear or branchedalkyl having 1 to 25 C-atoms, wherein one or more non-adjacent —CH₂—groups, independently of each another, may be replaced by—C(R⁰)═C(R⁰⁰)—, —C≡C—, —N(R⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—in such a way that neither O- nor S-atoms are directly linked to oneanother, and wherein also one or more H-atoms may be replaced by F, Cl,CN or P¹-Sp¹-, R⁰, R⁰⁰ are each, at each occurrence independently of oneanother, H or alkyl having 1 to 12 C-atoms, L is at each occurrenceindependently of one another, F, Cl, CN, SCN, SF₅ or linear or branched,optionally mono- or poly-fluorinated, alkyl, alkoxy, alkenyl, alkinyl,alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxyhaving 1 to 12 C-atoms, and r is 0, 1, 2, 3 or
 4. 10. Method ofstabilisation of a mesogenic medium wherein a medium according to claim7 is subjected to polymerisation of its polymerisable constituents. 11.Mesogenic medium stabilised by the polymerisation of the polymerisableconstituents of a medium according to claim
 7. 12. Light modulationelement, characterized in that it comprises a medium according claim 1.13. Electro-optical display, characterized in that it comprises a mediumaccording to claim
 1. 14. A method of using a medium according to claim1, comprising incorporating said medium in a light modulation element.